Browsing by Author "Jordan, Ryan N."

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Enhanced mobility of pb in the presence of dissolved natural organic matter
(1997-12) Jordan, Ryan N.; Yonge, David R.; Hathhorn, Wade E.
The speciation of Pb in batch experiments and its mobility under flowing conditions in column transport experiments were investigated to study Pb behavior in a soil-water system in the presence of dissolved natural organic matter (DOM), peat humic acid (PHA) and peat fulvic acid (PFA). A sandy soil having a significant intraparticle porosity was used as the sorbing media. Batch equilibrium sorption isotherms for single components (Pb, PHA, and PFA) and for Pb in the presence of PHA and PFA were generated. Batch equilibrium experiments were also performed for both PHA and PFA to investigate Pb-DOM binding in the absence of soil. Single component (Pb, PHA, and PFA) and multicomponent (Pb-PHA and Pb-PFA) laboratory-scale column transport experiments were conducted to assess transport behavior of Pb in the presence of DOM. Sorption isotherms indicated that the soil had a higher affinity for PHA than for PFA. However, single component column transport experiments showed that PHA was less retarded than PFA. This anomaly was attributed to the size exclusion of the larger PHA molecules from the intraparticle porosity of the media under the geochemical conditions in the column. Pb retardation predicted by equilibrium equations based upon nonlinear isotherm parameterization agreed well with observed retardation. However, equilibrium retardation equations overpredicted retardation of DOM, indicating sorption kinetic limitations (chemical and/or physical nonequilibrium), molecular size exclusion during column transport, or chemical heterogeneity of the DOM. In multicomponent column transport experiments, Pb retardation decreased by factors of 4–8 in the presence of DOM. Multicomponent batch equilibrium experiments suggested that Pb mobility was governed by speciation of Pb with soluble DOM during transport. Thus, Pb eluted earlier in the presence of PHA than in the presence of PFA because PHA had a higher affinity for Pb binding than PFA.
Evaluating biofilm activity in response to the mass transfer-limited bioavailability of sorbed nutrients
(1999) Jordan, Ryan N.
The role of (bio)surfactant sorption in promoting the bioavailability of nutrients localized at the solid-water interface
(1999) Jordan, Ryan N.; Nichols, E. P.; Cunningham, Alfred B.
Bioavailability is herein defined as the accessibility of a substrate by a microorganism. Further, bioavailability is governed by (1) the substrate concentration that the cell membrane “sees,” (i.e., the “directly bioavailable” pool) as well as (2) the rate of mass transfer from potentially bioavailable (e.g., nonaqueous) phases to the directly bioavailable (e.g., aqueous) phase. Mechanisms by which sorbed (bio)surfactants influence these two processes are discussed. We propose the hypothesis that the sorption of (bio)surfactants at the solid-liquid interface is partially responsible for the increased bioavailability of surface-bound nutrients, and offer this as a basis for suggesting the development of engineered in-situ bioremediation technologies that take advantage of low (bio)surfactant concentrations. In addition, other industrial systems where bioavailability phenomena should be considered are addressed.
Surfactant-enhanced bioremediation: a review of the effects of surfactants on the bioavailability of hydrophobic organic chemicals in soils
(1999) Jordan, Ryan N.; Cunningham, Alfred B.