Microbial Sulfate Reduction and Perchlorate Inhibition in a Novel Mesoscale Tank Experiment

Microbial
sulfate reduction occurs ubiquitously in natural environments.
In oil and gas reservoirs, the generation of sulfide (also known as
souring) can result in the corrosion of steel infrastructure and downgrading
of oil quality, among other environmental and health-related concerns.
The complex interplay between hydrological, geochemical, and biological
processes during souring is poorly understood, preventing effective
treatment and mitigation especially in naturally heterogeneous subsurfaces.
In this work, three-dimensional flow tank experiments are utilized
as a mesoscale experiment that links well-constrained batch and column
experiments to field measurements. The mesoscale tank experiment investigating
perchlorate treatment of souring is coupled with reactive transport
modeling to understand the effects of heterogeneity on souring and
effectiveness of perchlorate treatment. Tracer experiments were conducted
at the start and end of the experiment to constrain flow pathways
and heterogeneities. Isotopic, geochemical, and microbial data revealed
that perchlorate effectively inhibited sulfidogenesis and the growth
of dominant sulfate reducing Desulfobacteraceae.
Perchlorate treatment enriched Desulfobulbaceae,
a sulfur-oxidizing group of bacteria, and Sulfurimonas, a potential perchlorate reducer. More organisms, including sulfate
reducing bacteria, were observed closer to the influent. Results from
the three-dimensional reactive transport model indicate horizontal
preferential flows, as a result of the permeability contrast, led
to faster bacteria growth (sulfate reducing bacteria) and sulfate
reduction in fast flow regions. This work highlights the control that
spatial distributions of hydrologic characteristics exert over reservoir
souring and treatment.