Leonard W. Lion

Phosphorus removal by wollastonite: A constructed wetland substrate

Wollastonite, a calcium metasilicate mineral mined in upstate New York, is an ideal substrate for constructed wetland ecosystems for removing soluble phosphorus from secondary wastewater. Design parameters, required for designing a full-scale constructed wetland, were measured in vertical upflow columns with hydraulic residence times varying from 15 to 180 h. Secondary wastewater was pumped vertically upward through eleven soil columns, 1.5 m in length and 15 cm in diameter and influent and effluent concentrations of soluble phosphorus were monitored for up to 411 days. Greater than 80% removal (up to 96%) was observed in nine out of 11 columns and effluent concentrations of soluble phosphorus ranged from 0.14 to 0.50 mg:l (averaging 0.28 mg:l) when the residence time was \40 h. Columns with a decreased residence time averaged 39% removal. A direct relationship between residence time and soluble phosphorus removal was established.

Effects of soil properties and moisture on the sorption of trichloroethylene vapor

Correlation of tricholoroethylene (TCE) vapor partition coefficients (at P/P0 < 2%) onto seven sorbents with selected properties showed that: (1) under oven-dried conditions, specific surface area best described sorption of TCE and (2) under air-dried conditions (68% r.h.), at field capacity and for saturated conditions, organic carbon content controlled sorption. The change in the dependency of TCE vapor partition coefficients, from specific surface area at oven-dried conditions to organic carbon content at air-dried conditions, is hypothesized to result from: (1) reduced sorption of TCE onto mineral surfaces because of competition with water and (2) increased importance of partitioning into organic matter. At field capacity, the sorption of TCE vapor can be accounted for by two contributions: (1) dissolution of TCE in the water bound to the sorbent as governed by Henrys law and (2) sorption of TCE at the solid-liquid interface as governed by a saturated partition coefficient. Dissolution of TCE into surface-bound water can constitute a large fraction of the total TCE uptake from the vapor phase for sorbents with low organic carbon content.

Mobilization of adsorbed cadmium and lead in aquifer material by bacterial extracellular polymers

The mobility of cationic trace metals, such as Pb and Cd, in porous media can be severely limited by their adsorption at the solid/solution interface. The transport of metals can be enhanced by complexation with a ligand of “carrier” that (i) is soluble in water and does not strongly sorb to surfaces, (ii) has a high metal binding affinity and (iii) is not readily altered in soil by chemical or biological reactions. Extracellular polymers of bacterial origin are plausible carriers for metals in soil or aquifer systems. Bacterial extracellular polymers occur naturally in groundwaters and some have well established metal binding properties. In this study, extracellular polymers from 13 bacterial strains, including five subsurface isolates, were screened for their ability to mobilize Pb and Cd adsorbed to an aquifer sand. Batch adsorption isotherms were employed to screen polymers for their effect on metal phase distribution. All of the extracellular polymers tested reduced the linear distribution coeffients of Cd and Pb. Reductions in metal adsorption by over 90% were achieved at an extracellular polymer concentration of 10.6 mg l−1 The sorption isotherm of a selected extracellular polymer indicated that it had a low affinity for the sand sorbent and suggested that the polymer would be mobile in the porous sand medium. The distribution coefficient of the polymer for the sand was not effected by the presence Cd at low concentrations. Independently determined distribution constants for Cd and extracellular polymer with the sand and the binding constant for Cd to polymer yielded reasonable estimates of the observed distribution of Cd in the presence of the extracellular polymer. Column experiments performed with Cd in the presence and absence of the selected extracellular polymer confirmed that application of polymer solutions can enhance metal mobility in porous media.

Influence of vapor-phase sorption and diffusion on the fate of trichloroethylene in an unsaturated aquifer system.

This research evaluates the influence of vapor-phase sorption and diffusion on the fate and transport of a common volatile pollutant, trichloroethylene (TCE). Vapor-phase sorption of TCE by a porous aluminum oxide surface coated with humic acids (to simulate an aquifer material) was observed to be highly dependent on moisture content. Linear partition coefficients for binding of TCE vapor under a range of unsaturated conditions were 1-4 orders of magnitude greater than the value measured for the saturated sorbent. In addition, laboratory measurement of the TCE diffusion coefficient through the simulated aquifer material indicated that an existing empirical formula used to estimate this parameter can be in error by as much as 400%. The significance of differences in sorptive partition coefficients and diffusion coefficients was examined with an existing one-dimensional vertical transport model for the unsaturated zone. Model calculations indicate that the common practice of assuming saturated partition coefficients apply to unsaturated conditions should be avoided to obtain accurate predictions of volatile contaminant transport.

Evaluation of sorptive partitioning of nonionic pollutants in closed systems by headspace analysis

An equilibrium headspace technique is shown to be applicable to the determination of sorption equilibria for the nonionic volatile organic compounds toluene and trichloroethylene (TCE). This procedure avoids the problems inherent in other experimental techniques that directly analyze aqueous phase concentration. Such problems include incomplete solid phase separation and subsequent measurements of solute bound to dissolved or colloidal sorbent as free solute. Sorptive partitioning coefficients may be determined by the headspace procedure in the absence of carrier solvents or knowledge of the aqueous concentration of the volatile compounds of concern. Experiments examining the sorption of toluene and TCE onto humic acids, alumina coated with humic acids, and two soil core samples demonstrated the applicability of the headspace technique to sorption studies.

Kinetics of Mn(II) oxidation by Leptothrix discophora SS1

The kinetics of Mn(II) oxidation by the bacterium Leptothrix discophora SS1 was investigated in this research. Cells were grown in a minimal mineral salts medium in which chemical speciation was well defined. Mn(II) oxidation was observed in a bioreactor under controlled conditions with pH, O2, and temperature regulation. Mn(II) oxidation experiments were performed at cell concentrations between 24 mg/L and 35 mg/L, over a pH range from 6 to 8.5, between temperatures of 10°C and 40°C, over a dissolved oxygen range of 0 to 8.05 mg/L, and with L. discophora SS1 cells that were grown in the presence of Cu concentrations ranging from zero to 0.1 μM. Mn(II) oxidation rates were determined when the cultures grew to stationary phase and were found to be directly proportional to O2 and cell concentrations over the ranges investigated. The optimum pH for Mn(II) oxidation was approximately 7.5, and the optimum temperature was 30°C. A Cu level as low as 0.02 μM was found to inhibit the growth rate and yield of L. discophora SS1 observed in shake flasks, while Cu levels between 0.02 and 0.1 μM stimulated the Mn(II) oxidation rate observed in bioreactors. An overall rate law for Mn(II) oxidation by L. discophora as a function of pH, temperature, dissolved oxygen concentration (D.O.), and Cu concentration is proposed. At circumneutral pH, the rate of biologically mediated Mn(II) oxidation is likely to exceed homogeneous abiotic Mn(II) oxidation at relatively low (≈μg/L) concentrations of Mn oxidizing bacteria.

Lead Distribution in a Simulated Aquatic Environment: Effects of Bacterial Biofilms and Iron Oxide

Abstract Biofilms influence the transport and fate of heavy metals in aquatic environments both directly by adsorption and complexation reactions and indirectly via interactions with oxides of iron and manganese. These reactions were investigated by introducing lead into a continuous-flow biofilm reactor that was designed to simulate conditions in a flowing freshwater aquatic environment. The reactor provided controlled conditions, and use of a chemically-defined growth medium allowed calculation of lead speciation with a chemical equilibrium program (MINEQL). Pseudomonas cepacia was employed as a test cell strain because of its ability to grow and form biofilms in the defined medium. This bacterium affected lead distribution in the reactor by adsorbing lead both to adherent and suspended cells. When the aqueous bulk lead concentration was 1.4 ± 0.1 μM and biofilm coverage (measured as chemical oxygen demand, COD) was 50 mequiv COD/m 2 , lead adsorption was increased by about a factor of five relative to bare glass. Of the total lead in solution, only 1% was adsorbed to suspended cells (5 × 10 7 cells/ml). Lead adsorption to biofilms followed a Langmuir isotherm with a maximum adsorption ( Γ max ) of 56 μmol Pb/equiv COD and an adsorption equilibrium constant ( K ) of 0.64 liter/μmol Pb. Lead complexed with dissolved bacterial expopolymer was below detection limits. Pretreatment of glass slides with colloidal iron also significantly increased lead adsorption relative to bare glass. Lead adsorption to adsorbed iron fit a Langmuir isotherm with Γ max = 50 μ mol Pb/mol fe, and K = 1.3 liter/μmol Pb. Lead binding to glass coated with both cells and iron was additive, and could be predicted by summing adsorption predicted using isotherms for each constituent. The presence of iron surface coatings increased initial biofilm formation rates, but after reaching steady state conditions, biofilm coverage was similar for slides treated with iron and untreated slides. A concentration of 1 μM lead produced a transient reduction in suspended cell counts. Cell counts recovered to the original cell density over the course of five to ten reactor retention times. With iron present, the magnitude of the reduction in cell concentration in response to the addition of lead was greatly reduced, suggesting that toxic effects of lead may be reduced by iron.

Functional tomographic fluorescence imaging of pH microenvironments in microbial biofilms by use of silica nanoparticle sensors.

ABSTRACT Attached bacterial communities can generate three-dimensional (3D) physicochemical gradients that create microenvironments where local conditions are substantially different from those in the surrounding solution. Given their ubiquity in nature and their impacts on issues ranging from water quality to human health, better tools for understanding biofilms and the gradients they create are needed. Here we demonstrate the use of functional tomographic imaging via confocal fluorescence microscopy of ratiometric core-shell silica nanoparticle sensors (C dot sensors) to study the morphology and temporal evolution of pH microenvironments in axenic Escherichia coli PHL628 and mixed-culture wastewater biofilms. Testing of 70-, 30-, and 10-nm-diameter sensor particles reveals a critical size for homogeneous biofilm staining, with only the 10-nm-diameter particles capable of successfully generating high-resolution maps of biofilm pH and distinct local heterogeneities. Our measurements revealed pH values that ranged from 5 to >7, confirming the heterogeneity of the pH profiles within these biofilms. pH was also analyzed following glucose addition to both suspended and attached cultures. In both cases, the pH became more acidic, likely due to glucose metabolism causing the release of tricarboxylic acid cycle acids and CO2. These studies demonstrate that the combination of 3D functional fluorescence imaging with well-designed nanoparticle sensors provides a powerful tool for in situ characterization of chemical microenvironments in complex biofilms.

Pb scavenging from a freshwater lake by Mn oxides in heterogeneous surface coating materials.

Selective extraction techniques were used to assay the importance of specific solid phases in Pb binding by heterogeneous surface coating materials (biofilms) in Cayuga Lake, NY. Hydroxylamine hydrochloride (NH(2)OH.HC1) was used to extract easily reducible Mn oxides, and sodium dithionite (Na(2)S(2)O(4)) was used to extract Mn and Fe oxides in two sets of biofilm samples retrieved from the lake. Pb remaining after extraction was removed by extraction with 10% HNO(3), determined by analysis of Pb(208) using a sector field mass spectrometer with an inductively coupled plasma ion source (ICP-MS), and compared to the total extractable Pb. The results indicate that the greatest contribution to total Pb binding to the heterogeneous surface coating materials was from Mn oxides. Pb adsorption capacity of Mn oxides exceeded that of Fe oxides on a molar basis by approximately an order of magnitude. The high reactivity observed for natural Mn oxides indicates that they are biogenic in origin, consistent with expectations based on the relative biotic and abiotic rates of Mn(II) oxidation under circumneutral conditions. Collectively, these results confirm expectations based on prior observations of adsorption of added Pb by Cayuga Lake biofilms before and after selective extraction, and also confirm predictions for Pb phase association in the lake based on the behavior of laboratory surrogates for adsorptive surfaces.

Turbulent coagulation of colloidal particles

Theoretical predictions for the coagulation rate induced by turbulent shear have often been based on the hypothesis that the turbulent velocity gradient is persistent (Saffman & Turner 1956) and that hydrodynamic and interparticle interactions (van der Waals attraction and electrostatic double-layer repulsion) between colloidal particles can be neglected. In the present work we consider the effects of interparticle forces on the turbulent coagulation rate, and we explore the response of the coagulation rate to changes in the Lagrangian velocity gradient correlation time (i.e. the characteristic evolution time for the velocity gradient in a reference frame following the fluid motion). Stokes equations of motion apply to the relative motion of the particles whose radii are much smaller than the lengthscales of turbulence (i.e. small particle Reynolds numbers). We express the fluid motion in the vicinity of a pair of particles as a locally linear flow with a temporally varying velocity gradient. The fluctuating velocity gradient is assumed to be isotropic and Gaussian with statistics taken from published direct numerical simulations of turbulence (DNS). Numerical calculations of particle trajectories are used to determine the rate of turbulent coagulation in the presence and absence of particle interactions. Results from the numerical simulations correctly reproduce calculated coagulation rates for the asymptotic limits of small and large total strain where total strain is a term used to describe the product of the characteristic strain rate and its correlation time. Recent DNS indicate that the correlation times for the fluctuating strain and rotation rate are of the same order as the Kolmogorov time (Pope 1990), suggesting theories that assume either small or large total strain may poorly approximate the turbulent coagulation rate. Indeed, simulations for isotropic random flows with intermediate total strain indicate that the coagulation rate in turbulence is significantly different from the analytical limits for large and small total strain. The turbulent coagulation rate constant for non-interacting monodisperse particles scaled with the Kolmogorov time and the particle radius is 8.62±0.02, whereas the commonly used model of Saffman & Turner (1956) predicts a value of 10.35 for non-rotational flows in the limit of persistent turbulent velocity gradients. Additional simulations incorporating hydrodynamic interactions and van der Waals attraction were used to estimate the actual rate of particle coagulation. For typical values of these parameters, particle interactions reduced the coagulation rate constant by at least 50%. In general, the collision efficiency (the ratio of coagulation with particle interactions to that without) decreased with increasing particle size and Kolmogorov shear rate.