Inducing mineral precipitation in groundwater by addition of phosphate

<p>Abstract</p> <p>Background</p> <p>Induced precipitation of phosphate minerals to scavenge trace elements from groundwater is a potential remediation approach for contaminated aquifers. The success of engineered precipitation schemes depends on the particular phases generated, their rates of formation, and their long term stability. The purpose of this study was to examine the precipitation of calcium phosphate minerals under conditions representative of a natural groundwater. Because microorganisms are present in groundwater, and because some proposed schemes for phosphate mineral precipitation rely on stimulation of native microbial populations, we also tested the effect of bacterial cells (initial densities of 10⁵and 10⁷mL^-1) added to the precipitation medium. In addition, we tested the effect of a trace mixture of propionic, isovaleric, formic and butyric acids (total concentration 0.035 mM).</p> <p>Results</p> <p>The general progression of mineral precipitation was similar under all of the study conditions, with initial formation of amorphous calcium phosphate, and transformation to poorly crystalline hydroxylapatite (HAP) within one week. The presence of the bacterial cells appeared to delay precipitation, although by the end of the experiments the overall extent of precipitation was similar for all treatments. The stoichiometry of the final precipitates as well as Rietveld structure refinement using x-ray diffraction data indicated that the presence of organic acids and bacterial cells resulted in an increasing <it>a </it>and decreasing <it>c </it>lattice parameter, with the higher concentration of cells resulting in the greatest distortion. Uptake of Sr into the solids was decreased in the treatments with cells and organic acids, compared to the control.</p> <p>Conclusions</p> <p>Our results suggest that the minerals formed initially during an engineered precipitation application for trace element sequestration may not be the ones that control long-term immobilization of the contaminants. In addition, the presence of bacterial cells appears to be associated with delayed HAP precipitation, changes in the lattice parameters, and reduced incorporation of trace elements as compared to cell-free systems. Schemes to remediate groundwater contaminated with trace metals that are based on enhanced phosphate mineral precipitation may need to account for these phenomena, particularly if the remediation approach relies on enhancement of <it>in situ </it>microbial populations.</p

Aligning business process reengineering in implementing global supply chain systems by the SCOR model

International audienceAs supply chains continue to replace individual companies as the management arena for value-adding from the beginning of the twenty first century, understanding the supply chain management practices in a globalization context becomes increasingly important. The Supply Chain Operations Reference (SCOR) Model, which was developed by the experts and practitioners of the Supply Chain Council, is a major framework for supply chain planning which features supply chain management practices and business process reengineering. Despite being an integrative guide with many merits, it only provides a ‘top-down' approach which requires the comparative analyses of post- and pro- performance indices as a basis of business process modification. This study discusses the limitations of current SCOR analysis and provides a mapping technique— Causes/Effects, the SCOR Standard, and Mutual Solution (CESM)—for gap mapping, problem prioritization, and business process modification in a supply chain setting. As such it is one of the early empirical studies combining BPR and SCM disciplines. The research results can facilitate the implementation processes of multinational supply chain projects by identifying the gaps and linking them to the channel entities