Transformation of 2-Line Ferrihydrite to Goethite at Alkaline pH.

The transformation of 2-line ferrihydrite to goethite from supersaturated solutions at alkaline pH ≥ 13.0 was studied using a combination of benchtop and advanced synchrotron techniques such as X-ray diffraction, thermogravimetric analysis, and X-ray absorption spectroscopy. In comparison to the transformation rates at acidic to mildly alkaline environments, the half-life, t1/2, of 2-line ferrihydrite reduces from several months at pH = 2.0, and approximately 15 days at pH = 10.0, to just under 5 h at pH = 14.0. The calculated-first order rate constants of transformation, k, increase exponentially with respect to the pH and follow the progression log10 k = log10 k0 + a·pH3. Simultaneous monitoring of the aqueous Fe(III) concentration via inductively coupled plasma optical emission spectroscopy demonstrates that (i) goethite likely precipitates from solution and (ii) its formation is rate-limited by the comparatively slow redissolution of 2-line ferrihydrite. The analysis presented can be used to estimate the transformation rate of naturally occurring 2-line ferrihydrite in aqueous electrolytes characteristic to mine and radioactive waste tailings as well as the formation of corrosion products in cementitious pore solutions.

Simulating waste temperatures in an operating landfill in Québec, Canada.

A bioreactor landfill operated in Sainte-Sophie, Québec, Canada was instrumented to better understand the waste stabilization process in northern climates. Instrument bundles were placed within the waste to monitor temperature, oxygen, moisture content, settlement, total load, mounding of leachate and electrical conductivity. A finite element model was developed to simulate the heat fluxes to and from the waste, as well as heat generation within the waste from both anaerobic and aerobic processes. The results of the analysis suggest the majority of the aerobic activity occurs in the top portion of the waste lift exposed to ambient air. In addition, the model indicates that frozen waste lifts require a significant amount of heat to thaw the liquid fraction. The model also demonstrates that when a lift of cold waste is placed at the bottom of the landfill, the subsurface acts as a significant source of heat.

Growth and characterization of Escherichia coli DH5α biofilm on concrete surfaces as a protective layer against microbiologically influenced concrete deterioration (MICD).

Biofilms of selected bacteria strains were previously used on metal coupons as a protective layer against microbiologically influenced corrosion of metals. Unlike metal surfaces, concrete surfaces present a hostile environment for growing a protective biofilm. The main objective of this research was to investigate whether a beneficial biofilm can be successfully grown on mortar surfaces. Escherichia coli DH5α biofilm was grown on mortar surfaces for 8 days, and the structure and characteristics of the biofilm were studied using advanced microscopy techniques such as scanning electron microscopy and confocal laser scanning microscopy in combination with fluorescence in situ hybridization, live/dead, extracellular polymer staining, ATP analysis, and membrane filtration. A biofilm layer with a varying thickness of 20-40 µm was observed on the mortar surface. The distribution of live and dead bacteria and extracellular polymers varied with depth. The density of the live population near the mortar surface was the lowest. The bacteria reached their highest density at three fourths of the biofilm depth and then decreased again near the biofilm-liquid interface. Overall, the results indicated a healthy biofilm growth in the chosen growth period of 8 days, and it is expected that longer growth periods would lead to formation of a more resistant biofilm with more coverage of mortar surfaces.

Modeling of biological clogging in unsaturated porous media.

A two-dimensional unsaturated flow and transport model, which includes microbial growth and decay, has been developed to simulate biological clogging in unsaturated soils, specifically biofilters. The bacterial growth and rate of solute reduction due to biodegradation is estimated using the Monod equation. The effect of microbial growth is considered in the proposed conceptual model that relates the relative permeability term for unsaturated flow to the microbial growth. Two applications of the model are presented in this study. Using the model, the clogging mechanism in different soils has been simulated. The results of the model indicate that the time to reach a clogged state is influenced by the hydraulic properties of the soil. Clogging is delayed in soils with higher saturated hydraulic conductivities, and higher porosities. For the relative permeability model proposed, higher van Genuchten n values lead to a delay in clogging. The model was also used to simulate the progressive clogging of a septic bed as the biomat initially forms at the up-gradient end of the distribution pipe, displacing wastewater infiltration and biomat formation further down-gradient over time.