Assessing the biodegradation of hydrocarbons by respirometry during biostimulation with nutrients in contaminated soils

During soil-remediation studies, biostimulation and
bioaugmentation are used to increase the degradation rate
of contaminants. Biodegradation can be evaluated by
respirometry (O2 consumption and CO2 production) to
determine the growth, activity of hydrocarbon-utilizing
microorganisms and treatment utilized. The oxygen consumption is proportional to the contaminant degraded.
Respirometry is a simple, cheap and fast method that can
be used with different contaminated matrices (soil, water
and sediments). During this study, O2 consumption of
hydrocarbon-contaminated soil (40,000 mg TPHkgps
1
) was
used to evaluate biostimulation by addition of inorganic
fertilizers (ICF) and inorganic salts (IS). Two different
types of respirometers (HACH and OXITOP) were
evaluated over 13 days utilizing a control with diesel as
reference substance. Physicochemical (pH, nutrients and
TPH) and microbiological analyses (heterotrophic and
hydrocarbon-utilizing microorganisms) were measured at
the beginning and end of each assay. The oxygen
consumption curves indicated that IS and the control
without nutrients had the maximum respiration rates in
HACH (802.3 and 850.7 mgO2 kgps
1 d1
, respectively) and
OXITOP (936.7 and 502.1 mgO2 kgps
1 d1
, respectively).
There was no significant increase in the hydrocarbonutilizer numbers in the treatments. ICF presented the
lowest respiration rates and microbial counts, showing an
inhibitory effect for the concentration and type used. The
use of respirometry allowed the determination of metabolic
activity and the effects of added nutrients in a short period
of time and indicated that high-molecular-weight hydrocarbons limited biodegradation.