Enhanced denitrification in groundwater and sediments from a nitrate-contaminated aquifer after addition of pyrite

Abstract

Using chemical, isotopic and microbiologic techniques we tested in laboratory experiments the extent to which the addition of pyrite to groundwater and sediments from a nitrate-contaminated aquifer could stimulate denitrification by indigenous bacteria. In addition to this biostimulated approach, a combined biostimulated and bioaugmented treatment was also evaluated by inoculating the well-known autotrophic denitrifying bacterium Thiobacillus denitrificans. Results showed that the addition of pyrite enhanced nitrate removal and that denitrifying bacteria existing in the aquifer material were able to reduce nitrate using pyrite as the electron donor, obviating the need for the inoculation of T. denitrificans. The results of the 16S rRNA and nosZ gene-based DGGE and the quantitative PCR (qPCR) showed that the addition of pyrite led to an increase in the proportion of denitrifying bacteria and that bacterial populations closely related to the Xanthomonadaceae might probably be the autotrophic denitrifiers that used pyrite as the electron donor. Not only autotrophic but also heterotrophic denitrifying bacteria were stimulated through pyrite addition and both populations probably contributed to nitrate removal. Isotopic analyses (δ 15 N and δ 18 ONO3) were used to monitor enhanced denitrification and the N and O isotopic enrichment factors (-26.3±1.8‰ and-20.4±1.3‰, respectively) allowed to calculate the degree of natural nitrate attenuation in the aquifer. Furthermore, flow-through experiments amended with pyrite confirmed the long-term efficiency of the process under the study conditions. Further research under field conditions is needed to determine whether stimulation of denitrification by pyrite addition constitutes a feasible bioremediation strategy for nitratecontaminated aquifers.

Modeling biogeochemical processes and isotope fractionation of enhanced in situ biodenitrification in a fractured aquifer

“…Assuming Monod degradation kinetics, the 274 rates of the heavy ( determined under laboratory conditions (closed system), they were only affected by 281 degradation processes, and they could be used at the field scale (Torrentó et al, 2011; Carrey 282 et al, 2013). Furthermore, laboratory conditions were very similar to field conditions: the 283 groundwater and sediments used were taken from the site and the in-situ groundwater 284 temperature (15ºC) was maintained.…”

Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer

“…However, a growing body of research suggests that denitrification in most aquifers depends on matrix-derived, solid-phase electron donors (e.g. Fe 2+ , H 2 S) rather than surface-derived solutes (Green et al, 2008;Schwientek et al, 2008;Zhang et al, 2009;Torrento et al, 2010Torrento et al, , 2011. As a result, concentrations of dissolved organic matter and other electron donors may be a poor indicator of denitrification rates across aquifers, and spatial patterns within aquifers may reflect the distribution of these reactants within the aquifer matrix rather than substrate depletion along advective flowpaths.…”

Determination of Denitrification Genes Abundance in Environmental Samples

“…Isolation and purification of DNA from aqueous samples usually requires concentration of the bacterial biomass by filtering the samples through 0.22-µm membranes and further homogenization of the filters [116]. Thermal shocks do not usually increase DNA yield and, in turn, may release humic material.…”