Groundwater systems are important sources of
water for drinking and irrigation purposes. Unfortunately,
human activities have led to widespread groundwater
contamination by chlorinated compounds such as tetrachloroethene
(PCE). Chloroethenes are extremely harmful
to humans and the environment due to their carcinogenic
properties. Therefore, this study investigated the potential
for bioremediating PCE-contaminated groundwater using
laboratory-based biostimulation (BS) and biostimulation–
bioaugmentation (BS-BA) assays. This was carried out on
groundwater samples obtained from a PCE-contaminated
site which had been unsuccessfully treated using chemical
oxidation. BS resulted in complete dechlorination by week
21 compared to controls which had only 30 % PCE degradation.
BS also led to a approximately threefold increase
in 16S rRNA gene copies compared to the controls.
However, the major bacterial dechlorinating group,
Dehalococcoides
(
Dhc), was undetectable in PCE-contaminated
groundwater. This suggested that dechlorination in
BS samples was due to indigenous non-
Dhc dechlorinators.
Application of the BS-BA strategy with
Dhc as the augmenting
organism resulted in complete dechlorination by
week 17 with approximately twofold to threefold increase
in 16S rRNA and
Dhc gene abundance. Live/dead cell
counts (LDCC) showed 70–80 % viability in both treatments
indicating active growth of potential dechlorinators.
The LDCC was strongly correlated with cell copy numbers
(
r > 0.95) suggesting its potential use for low-cost monitoring
of bioremediation. This study also shows the dechlorinating
potential of indigenous non-
Dhc groups can be
successfully exploited for PCE decontamination while
demonstrating the applicability of microbiological and
chemical methodologies for preliminary site assessments
prior to field-based studies.