Immobilization of inorganic species by reactive porous media: Control of trace metals in a constructed urban marsh and fluoride removal via novel calcite hydroxyapatite

Ch1&2: Two tidal marshes in the New Jersey Meadowlands, constructed and natural, were characterized to compare their ability to immobilize trace metals (Cd, Cr, Cu, Mn, Pb, and Zn). Surface and pore-waters were sampled seasonally between 2008 and 2010 and sediment cores were collected yearly in the constructed marsh and once in 2010 in the natural marsh. Interactions of trace metals with redox active species (iron and sulfide) and with organic matter were investigated. Precipitation with sulfides played a major role in immobilizing Cr, Mn, and Pb. The presence of sulfide did not preclude the presence of dissolved trace metals in pore-water at concentrations exceeding their metal sulfide solubility product. Thermodynamic equilibrium modeling indicated these dissolved metals remained in solution due to an association with heterogeneous dissolved organic carbon. No net trace metal accumulation in the surficial sediments of the constructed marsh was noted. This implied that a dynamic equilibrium of trace metal flux into and out of the sediments was established, rather than a long-term net accumulation of trace metals. In the constructed marsh, little difference was found between the immobilization potential in the area of intermittent flooding and the area of sustained flooding. The newly constructed wetland immobilized significantly more Cr, Mn, and Zn than the natural marsh and similar concentrations of Cd, Cu, and Pb. This may be due to increased redox buffering through a larger FeS buffering pool against tidally induced oxygen delivery.;Ch3: To prevent health effects caused by drinking excessive fluoride in groundwater, a novel and economical hydroxyapatite-calcite material was developed. A lab-scale filter was studied to generate model parameters for optimization of a one-dimensional advective-dispersive-sorption transport model with instantaneous, kinetically limited, or multi-site adsorption. Then real-life operating conditions were simulated to predict column lifetimes and adsorption efficiency. HAC outperforms conventional bone char adsorbent and further material improvements are ongoing. Household-scale applications are viable and HAC was found to be an efficient alternative for removing fluoride from groundwater.