Biomedical subjects

S G Benner

Publications and source records attributed to S G Benner.

3 recordsLinked to original sources

PubMed2006

Process-based reactive transport modeling of a permeable reactive barrier for the treatment of mine drainage.

Reactive transport modeling of a permeable reactive barrier for the treatment of mine drainage was used to integrate a comprehensive data set including pore water chemistry and solid phase data from several sampling events over a >3-year time period. The simulations consider the reduction of sulfate by the organic carbon-based treatment material and the removal of sulfate and iron by precipitation of reduced mineral phases including iron monosulfides and siderite. Additional parameters constraining the model include dissolved H2S, alkalinity and pH, as well as a suite of solid phase S-fractions identified by extractions. Influences of spatial heterogeneity necessitated the use of a 2-dimensional modeling approach. Simulating observed seasonal fluctuations and long-term changes in barrier reactivity required the use of temperature dependent rate coefficients and a multimodal Monod-type rate expression accounting for the variable reactivity of different organic carbon fractions. Simulated dissolved concentrations of SO4, Fe, H2S, alkalinity and pH, as well as solid phase accumulations of reduced sulfur phases generally compare well to observed trends over 23 months. Spatial variations, seasonal fluctuations and the time-dependent decline in reactivity were also captured. The modeling results generally confirm, and further strengthen, the existing conceptual model for the site. Overall sulfate reduction and S-accumulation rates are constrained with confidence within a factor of 1.5.

Hydrogen-Ion Concentration↗

PubMed2001

Reactive transport modeling of processes controlling the distribution and natural attenuation of phenolic compounds in a deep sandstone aquifer.

Reactive solute transport modeling was utilized to evaluate the potential for natural attenuation of a contaminant plume containing phenolic compounds at a chemical producer in the West Midlands, UK. The reactive transport simulations consider microbially mediated biodegradation of the phenolic compounds (phenols, cresols, and xylenols) by multiple electron acceptors. Inorganic reactions including hydrolysis, aqueous complexation, dissolution of primary minerals, formation of secondary mineral phases, and ion exchange are considered. One-dimensional (1D) and three-dimensional (3D) simulations were conducted. Mass balance calculations indicate that biodegradation in the saturated zone has degraded approximately 1-5% of the organic contaminant plume over a time period of 47 years. Simulations indicate that denitrification is the most significant degradation process, accounting for approximately 50% of the organic contaminant removal, followed by sulfate reduction and fermentation reactions, each contributing 15-20%. Aerobic respiration accounts for less than 10% of the observed contaminant removal in the saturated zone. Although concentrations of Fe(III) and Mn(IV) mineral phases are high in the aquifer sediment, reductive dissolution is limited, producing only 5% of the observed mass loss. Mass balance calculations suggest that no more than 20-25% of the observed total inorganic carbon (TIC) was generated from biodegradation reactions in the saturated zone. Simulations indicate that aerobic biodegradation in the unsaturated zone, before the contaminant entered the aquifer, may have produced the majority of the TIC observed in the plume. Because long-term degradation is limited to processes within the saturated zone, use of observed TIC concentrations to predict the future natural attenuation may overestimate contaminant degradation by a factor of 4-5.

Aerobiosis↗

PubMedDate not supplied

Modeling preferential flow in reactive barriers: implications for performance and design.

Reactive barriers are passive and in situ ground water treatment systems. Heterogeneities in hydraulic conductivity (K) within the aquifer-reactive barrier system will result in higher flux rates, and reduced residence times, through portions of the barrier. These spatial variations in residence time will affect the treatment capacity of the barrier. A numerical flow model was used to evaluate the effects of spatial variations in K on preferential flow through barriers. The simulations indicate that the impact of heterogeneities in K will be a function of their location and distribution; the more localized the high K zone, the greater the preferential flow. The geometry of the reactive barrier will also strongly influence flow distribution. Aquifer heterogeneities will produce greater preferential flow in thinner barriers compared to thicker barriers. If the barrier K is heterogeneous, greater preferential flow will occur in thicker barriers. The K of the barrier will affect the flow distribution; decreasing the K of the barrier can result in more even distribution of flow. Results indicate that less variable flow will be attained utilizing thicker, homogeneous barriers. The addition of homogeneous zones to thinner barriers will be effective at redistributing flow only if installed immediately adjacent to both the up- and downgradient faces of the barrier.

Equipment Design↗