Abstract
Towards chlorinated solvents, the effectiveness of the remediation strategy can be improved by combining a biological approach (e.g., anaerobic reductive dechlorination) with chemical/physical treatments (e.g., adsorption). A coupled adsorption and biodegradation (CAB) process for trichloroethylene (TCE) removal is proposed in a biofilm–biochar reactor (BBR) to assess whether biochar from pine wood (PWB) can support a dechlorinating biofilm by combining the TCE (100 µM) adsorption. The BBR operated for eight months in parallel with a biofilm reactor (BR)—no PWB (biological process alone), and with an abiotic biochar reactor (ABR)—no dechlorinating biofilm (only an adsorption mechanism). Two flow rates were investigated. Compared to the BR, which resulted in a TCE removal of 86.9 ± 11.9% and 78.73 ± 19.79%, the BBR demonstrated that PWB effectively adsorbs TCE and slows down the release of its intermediates. The elimination of TCE was quantitative, with 99.61 ± 0.79% and 99.87 ± 0.51% TCE removal. Interestingly, the biomarker of the reductive dechlorination process, Dehalococcoides mccartyi, was found in the BRR (9.2 × 105 16S rRNA gene copies/g), together with the specific genes tceA, bvcA, and vcrA (8.16 × 106, 1.28 × 105, and 8.01 × 103 gene copies/g, respectively). This study suggests the feasibility of biochar to support the reductive dechlorination of D. mccartyi, opening new frontiers for field-scale applications.
Highlights
Chlorinated aliphatic hydrocarbons (CAHs) are some of the most common soil and groundwater contaminants, due to their chemical properties, production, and cost-effective uses [1,2]
This study aimed to evaluate the performance of the coupled adsorption and biodegradation (CAB) process with regards to the effectiveness of the biochar in sustaining the biological dechlorination, as well as monitoring the occurrence of the main dechlorinating microorganism D. mccartyi
A third abiotic reactor, which we will refer to as the “abiotic biochar reactor” (ABS), was prepared to the biofilm–biochar reactor (BBR) to observe the behavior of the TCE adsorption mechanism alone on pine wood biochar (PWB), with no dechlorinating biomass
Summary
Chlorinated aliphatic hydrocarbons (CAHs) are some of the most common soil and groundwater contaminants, due to their chemical properties, production, and cost-effective uses [1,2]. Spills, and the storage of these solvents in the subsoil have caused the contamination of several environmental matrices [3]. By the late 1960s, the public became more aware of environmental issues, such that perchloroethylene (PCE), trichloroethylene (TCE), and tetrachloroethane (TeCA) were identified as harmful pollutants [4]. Years of field experience, based on pump-and-treat, have shown that this technology achieves a significant reduction in CAH concentrations in aquifers. The adsorbed mass of the solvents may persist in the aquitard and less permeable areas, acting as a secondary source of contamination [2,5]. More sustainable and less energy-intense technologies are required to address CAH contamination [6]. Numerous advantages make in-situ bioremediation technologies an attractive and environmentally friendly choice [7]
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