School of Civil and Resource Engineering

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    Biocontainment of polychlorinated biphenyls (PCBs) on flat concrete surfaces by microbial carbonate precipitation
    (2015-09-02) Okwadha, George
    In this study, a biosealant obtained from microbial carbonate precipitation (MCP) was evaluated as an alternative to an epoxy-coating system. A bacterium Sporosarcina pasteurii strain ATCC 11859, which metabolizes urea and precipitates calcite in a calcium-rich environment, was used in this study to generate the biosealant on a PCB-contaminated concrete surface. Concrete cylinders measuring 3 in (76.2 mm) by 6 in (152.4 mm) were made in accordance with ASTM C33 and C192 and used for this purpose. The PCB, urea, Ca2þ, and bacterial cell concentrations were set at 10 ppm, 666 mM, 250 mM, and about 2.1 108 cells mL 1, respectively. The results indicate that the biosealed surfaces reduced water permeability by 1e5 orders of magnitude, and had a high resistance to carbonation. Since the MCP biosealant is thermally stable under temperatures of up to 840 C, the high temperatures that normally exist in the surrounding equipment, which may contain PCB-based fluids, have no effect on the biosealed surfaces. Consequently, there is greater potential to obtain a stronger, coherent, and durable surface by MCP. No measurable amount of PCBs was detected in the permeating water, indicating that the leaching water, if any, will have a minimum impact on the surrounding environment.
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    Evaluation of Surface Water Runoff from Fly Ash–Stabilized and Nonstabilized Soil Surfaces
    (2015-09-02) Okwadha, George
    This study evaluated the constituent make up of simulated rainwater runoff from Class C fly ash–stabilized and nonstabilized clay soil using laboratory test pads to assess the potential for impacts to surface water from the use of uncovered fly ash–stabilized soils as potential roadbed material. Recirculated runoff from test pads was sampled and tested during three simulated rainfall events over an 84-day trial period. All samples were analyzed for trace metals. Analytical results from the simulated runoff were screened to identify five indicator parameters in the runoff that were used as the basis for assessing potential environmental effects to surface waters. Runoff water results from fly ash–stabilized test pads for these indicator parameters were compared to water quality benchmarks. Based on the low concentrations measured in runoff relative to applicable criteria, and on the conservative nature of the experimental methods relative to typical field conditions, we concluded that surface runoff from fly ash–stabilized soil would not present significant adverse effects to surface water if used uncovered on low traffic exposed surfaces.
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    Institutional challenges in scaling-up climate change adaptation actions: experiences from rural communities in Senegal and Kenya
    (2017-09-27) Olang, Luke O.; Ouma, Gilbert O.; Dieye, Amadou M.; Ogallo, Laban O.
    Regional institutions in Africa have the potential to reinforce the adaptive capacity of rural communities in handling climate change impacts. The institutional arrangements provide the rationale for scaling-up adaptation actions by setting the roles of individual players involved in the planning process at local, national and regional levels. The scaling-up then seeks to extend and disseminate the lessons learnt across the levels to support refinement and inclusive implementation of long-term climate change adaptation strategies. This article discusses these considerations through studies of two rural communities faced with the implementation of climate change adaptation strategies in Senegal and Kenya. The cases illustrate different approaches of institutional arrangements and scaling-up of adaptation actions from community to national levels. The lessons from the communities are typical of most vulnerable rural regions and were hence important for extended dissemination considering that the impacts of climate change in Africa are felt largely at community levels. A reduction of this vulnerability requires efficient and realistic adaptation strategies that seek to understand the rural communities while developing considerate policy-based alternatives at all levels of administration.
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    Optimum conditions for microbial carbonate precipitation
    (2015-09-02) Okwadha, George
    The type of bacteria, bacterial cell concentration, initial urea concentration, reaction temperature, the initial Ca2+ concentration, ionic strength, and the pH of the media are some factors that control the activity of the urease enzyme, and may have a significant impact on microbial carbonate precipitation (MCP). Factorial experiments were designed based on these factors to determine the optimum conditions that take into consideration economic advantage while at the same time giving quality results. Sporosarcina pasteurii strain ATCC 11859 was used at constant temperature (25 C) and ionic strength with varying amounts of urea, Ca2+, and bacterial cell concentration. The results indicate that the rate of ureolysis (kurea) increases with bacterial cell concentration, and the bacterial cell concentration had a greater influence on kurea than initial urea concentration. At 25 mM Ca2+ concentration, increasing bacterial cell concentration from 106 to 108 cells mL 1 increased the CaCO3 precipitated and CO2 sequestrated by over 30%. However, when the Ca2+ concentration was increased 10-fold to 250 mM Ca2+, the amount of CaCO3 precipitated and CO2 sequestrated increased by over 100% irrespective of initial urea concentration. Consequently, the optimum conditions for MCP under our experimental conditions were 666 mM urea and 250 mM Ca2+ at 2.3 108 cells mL 1 bacterial cell concentration. However, a greater CaCO3 deposition is achievable with higher concentrations of urea, Ca2+, and bacterial cells so long as the respective quantities are within their economic advantage. X-ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray analyzes confirmed that the precipitate formed was CaCO3 and composed of predominantly calcite crystals with little vaterite crystals.
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    Spatial Modelling of Solar Energy Potential in Kenya
    (2017-09-27) Oloo Francis; Olang, Luke; Strobl, Josef
    Solar energy is one of the readily available renewable energy resources in the developing countries within the tropical region. Kenya is one of the countries which receive an average of approximately 6.5 sunshine hours in a single day throughout the year. However, there is slow adoption of solar energy resources in the country due to limited information on the spatial variability solar energy potential. This study aims at assessing the potential of photovoltaic solar energy in Kenya. The factors that influence incident solar radiation which were considered in this task included atmospheric transmissivity and topography. The influence of atmospheric transmissivity was factored in by modeling monthly transmissivity factors from a combination of cloud cover, diffuse ratios and the effect of altitude. The contribution of topography was included by applying hemispherical view shed analysis to determine the amount of incident global radiation on the surface based on the orientation of the terrain. GIS concepts were used to integrate the spatial datasets from different themes. The results showed that, about 70% of the land area in Kenya has the potential of receiving approximately 5 kWh/m2/day throughout the year. In outline, this work successfully assessed the spatio-temporal variability in the characteristics of solar energy potential in Kenya and can be used as a basis for policy support in the country.
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    Thermal Removal of Mercury in Spent Powdered Activated Carbon from TOXECON Process
    (2015-09-02) Okwadha, George
    This research developed and demonstrated a technology to liberate Hg adsorbed onto powdered activated carbon PAC by the TOXECON process using pilot-scale high temperature air slide HTAS and bench-scale thermogravimetric analyzer TGA . The HTAS removed 65, 83, and 92% of Hg captured with PAC when ran at 900°F, 1,000°F, and 1,200°F, respectively, while the TGA removed 46 and 100% of Hg at 800°F and 900°F, respectively. However, addition of CuO–Fe2O3 mixture and CuCl catalysts enhanced Hg removal and PAC regeneration at lower temperatures. CuO–Fe2O3 mixture performed better than CuCl in PAC regeneration. Scanning electron microscopy images and energy dispersive X-ray analysis show no change in PAC particle aggregation or chemical composition. Thermally treated sorbents had higher surface area and pore volume than the untreated samples indicating regeneration. The optimum temperature for PAC regeneration in the HTAS was 1,000°F. At this temperature, the regenerated sorbent had sufficient adsorption capacity similar to its virgin counterpart at 33.9% loss on ignition. Consequently, the regenerated PAC may be recycled back into the system by blending it with virgin PAC.