Site-specific pre-evaluation of bioremediation technologies for chloroethene degradation

Abstract

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 biostimulationbioaugmentation (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.

Exploiting the intrinsic microbial degradative potential for field-based in situ dechlorination of trichloroethene contaminated groundwater

“…This was likely due to the combined effects of nutrients and Dhc addition. Earlier work by Patil et al [20] which was laboratory based did show that a BS-BA combination increased the abundance of the dechlorinating community compared to other treatments [9]. Although these key dechlorinators were also detected the MNA wells, their rate of increase in abundance was comparatively lower.…”

“…Given that an indigenous dechlorinating community was already present, biostimulation alone or combined with bioaugmentation were effective treatment approaches as the existing dechlorination potential was enhanced by these treatments [20]. This was why the BS-BA approach (alongside the BS strategy) caused accelerated depletion of TCE species and substantial dechlorination of VC compared to MNA samples.…”

“…Using a laboratory based combined microbial and analytical approach can be helpful in designing effective in-situ bioremediation strategies [20]. Several laboratory studies have extensively assessed the role of Dhc mixed cultures for chloroethene removal by using molecular biological tools (MBTs).…”

“…There are very few reports of NGS based dechlorinating microbial community studies [26,27], with limited reports of NGS based in-situ remediation study [28]. Fundamental knowledge of microbial community structure, dynamics and functionality is important for predicting contaminant degradation patterns and deciding which bioremediation strategy to implement [20]. Metagenomics, PCR-DGGE and qPCR can be effectively used to assess the overall remediation progress by studying microbial shifts and correlating dechlorination rates with specific or total community response during in situ trials.…”

Nanoparticles for environmental clean-up: A review of potential risks and emerging solutions

“…Further a field in Victoria and South Australia, Australia the use of chlorinated compounds as thinners, cleaning and adhesive chemicals by the foam manufacturing industries has led to the formation of dense non-aqueous phase liquid (DNAPL) pools contaminating several groundwater aquifers over 3.5ha (Patil et al, 2014a). Earlier research carried out by Patil et al (2014a), Patil et al (2014b), Patil et al (2013) and Adetutu et al (2015) have reported the efficacy of a variety of methods for biological treatment of groundwater plumes from chloroethene contaminated site in Victoria, Australia. Following the recent successful trend of using these biological systems including bioremediation, phytoremediation and rhizoremediation, nanotechnology has recently been applied to environmental remediation (termed nanoremediation).…”