Carol J. Ptacek

Removal of agricultural nitrate from tile-drainage effluent water using in-line bioreactors

Abstract Two 200-L fixed-bed bioreactors, containing porous-medium material of coarse sand and organic carbon (tree bark, wood chips and leaf compost), were used to treat NO 3 contamination from agricultural runoff. Flow from a farm-field drainage tile containing NO 3 -N concentrations of 3–6 mg L −1 was successfully treated in the reactors (NO 3 -N −1 ) at a rate of 10–60 L day −1 over a 1-yr period. Treatment occurs by anaerobic denitrification promoted by the added solid-phase organic carbon. Because the reactor design is simple, economical to construct and maintenance free, it may provide a practical solution to the problem of treating redox-sensitive contaminants, such as NO 3 , in agricultural runoff.

Diavik waste rock project : blasting residuals in waste rock piles

Mining generates and moves the highest volume of material in the world. At mine sites throughout the world, explosives are used to fragment rock into workable size fractions. Mine-water chemistry can be influe nced by residual blasting agents used during mining. Ongoi ng monitoring of the water chemistry from three lar ge-scale waste rock test piles, measuring 60 by 50 m in area and 15 m high, began in 2007 and the quality of wa ter draining from this material is being studied. Blast ing residuals comprised a large proportion of disso lved constituents in the pore water and effluent for the first three monitoring seasons. Variations in con centrations and the gradual rates of dissipation of blasting re siduals provide an indication of the pile heterogen eity and the relative contribution of different flow paths. As temperatures within the piles increase with ambient temperature increases, larger proportions of the pile contribut e to flow, and increased concentrations of blasting residuals are observed in waste rock effluent. Mass-balance calc ulations based on the ratios of SO 4:Total-N can be used to estimate the relative contributions of sulfide oxid ation within the piles and sulfate released when su lfur in the host rock is oxidized during blasting. These calcu lations can also provide an estimate of S mass rele ased during the first flush of the piles. This research will a id in understanding the release of constituents cau sed by blasting and waste-rock hydrology.