Effect of copper, arsenic and nickel on pyrite-based autotrophic denitrification

Abstract

Pyritic minerals generally occur in nature together with other trace metals as impurities, that can be released during the ore oxidation. To investigate the role of such impurities, the presence of copper (Cu(II)), arsenic (As(III)) and nickel (Ni(II)) during pyrite mediated autotrophic denitrification has been explored in this study at 30 °C with a specialized microbial community of denitrifiers as inoculum. The three metal(loid)s were supplemented at an initial concentration of 2, 5, and 7.5 ppm and only Cu(II) had an inhibitory effect on the autotrophic denitrification. The presence of As(III) and Ni(II) enhanced the nitrate removal efficiency with autotrophic denitrification rates between 3.3 [7.5 ppm As(III)] and 1.6 [7.5 ppm Ni(II)] times faster than the experiment without any metal(loid) supplementation. The Cu(II) batches, instead, decreased the denitrification kinetics with 16, 40 and 28% compared to the no-metal(loid) control for the 2, 5 and 7.5 ppm incubations, respectively. The kinetic study revealed that autotrophic denitrification with pyrite as electron donor, also with Cu(II) and Ni(II) additions, fits better a zero-order model, while the As(III) incubation followed first-order kinetic. The investigation of the extracellular polymeric substances content and composition showed more abundance of proteins, fulvic and humic acids in the metal(loid) exposed biomass.

Keywords: Copper inhibition; Extracellular polymeric substances; Metals; Nitrate; Toxicity.

Fig. 1

Evolution of nitrate concentration with time during pyrite-based autotrophic denitrification in presence of A Cu(II), B As(III) and C Ni(II)

Fig. 2

Total soluble A Cu(II), B As(III), and C Ni(II) profiles during the pyrite-based autotrophic denitrification experiments in the 2 ppm (pink color filled circle), 5 ppm (green triangle), 7 ppm (yellow square) incubations and no-pyrite 2 ppm control (red colored diamond). (Color figure online)

Fig. 3

Evolution of electron shuttling capacity (ESC) of A no-metal control, B Cu(II), C As(III) and D Ni(II) experiments during pyrite-based autotrophic denitrification in the 2 ppm (pink triangle), 5 ppm (green square), and 7 ppm (yellow diamond) incubations. (Color figure online)

Fig. 4

3D Fluorescence Excitation Emission Matrix (FEEM) spectra of Cu(II) incubations at A 2 ppm, B 5 ppm, C 7.5 ppm; As(III) incubations at D 2 ppm, E 5 ppm, F 7.5 ppm and Ni(II) incubations at G 2 ppm, H 5 ppm, I 7.5 ppm. The color scale corresponds to the intensity of the peaks, which correlates to their concentration, where red/orange correspond to the highest intensity and blue corresponds to the lowest intensity. (Color figure online)