The bioelectric well: a novel approach for in situ treatment of hydrocarbon‐contaminated groundwater

Abstract

SummaryGroundwater contamination by petroleum hydrocarbons (PHs) is a widespread problem which poses serious environmental and health concerns. Recently, microbial electrochemical technologies (MET) have attracted considerable attention for remediation applications, having the potential to overcome some of the limiting factors of conventional in situ bioremediation systems. So far, field‐scale application of MET has been largely hindered by the limited availability of scalable system configurations. Here, we describe the ‘bioelectric well’ a bioelectrochemical reactor configuration, which can be installed directly within groundwater wells and can be applied for in situ treatment of organic contaminants, such as PHs. A laboratory‐scale prototype of the bioelectric well has been set up and operated in continuous‐flow regime with phenol as the model contaminant. The best performance was obtained when the system was inoculated with refinery sludge and the anode potentiostatically controlled at +0.2 V versus SHE. Under this condition, the influent phenol (25 mg l−1) was nearly completely (99.5 ± 0.4%) removed, with an average degradation rate of 59 ± 3 mg l−1 d and a coulombic efficiency of 104 ± 4%. Microbial community analysis revealed a remarkable enrichment of Geobacter species on the surface of the graphite anode, clearly pointing to a direct involvement of this electro‐active bacterium in the current‐generating and phenol‐oxidizing process.

Structure and Functions of Hydrocarbon-Degrading Microbial Communities in Bioelectrochemical Systems

“…Three different hydrocarbons were used as substrates in the three herein described experiments: Phenol [16], toluene [17], and a mixture of BTEX [18]. Two different inocula were tested: An activated sludge from a municipal wastewater treatment plant and a refinery wastewater.…”

“…The activated sludge was tested only in the experiment with phenol. Due to the low initial phenol removal performances and the low attained current densities, the reactor was successively re-inoculated with the refinery wastewater [16]. Samples from both inocula (activated sludge and refinery wastewater) and from the anodic graphite granules were collected during the experimental phases of the three separated experiments.…”

“…The bioelectrochemical experiments were carried out using 250-mL glass-cylinder membrane-less reactors, henceforth termed the 'bioelectric well', that were set and operated as previously described [16]. The glass cylinder was filled with graphite granules, serving as the bioanode, and housing a concentric stainless-steel mesh (90 cm 2 geometric surface area), serving as the cathode.…”

Operation of a 2-Stage Bioelectrochemical System for Groundwater Denitrification

“…The system was tested in laboratory scale achieving satisfactory results, however, with some adaptations groundwater treatment with BES technology could also become a feasible option for in situ denitrification. Different strategies have been reported by other researchers for in situ treatment of different contamination plumes, for example, the treatment of hydrocarbon-contaminated aquifers, such as the insertion of permeable barriers in confined or unconfined aquifers to provide treatment exploiting the natural flow of the water [62]. Cecconet et al [52] recently analyzed the estimated energy demands related to the application of similar systems of controlled biocathodic denitrification in ex situ on-site and in situ modes.…”

Bioelectrochemical Systems for Removal of Selected Metals and Perchlorate from Groundwater: A Review

“…BESs have been proposed for in situ application due to the possibility of using the electrodes as virtually inexhaustible electron acceptor and donor, without the need to add expensive chemicals that may also further contaminate the water resource [44]; to do so, research should focus on the development of a specially designed BES setup. Some attempts in doing so have been reported for hydrocarbons [159] and nitrate [160][161][162] removal, but more research should conducted to allow the presence of optimal conditions for bioelectroremediation (e.g., continuous contact between substrate and microorganisms, pH control).…”