Electrolysis-driven bioremediation of crude oil-contaminated marine sediments.

Bioremediation is an effective technology to tackle crude oil spill disasters, which takes advantage of the capacity of naturally occurring microorganisms to degrade petroleum hydrocarbons under a range of environmental conditions. The enzymatic process of breaking down oil is usually more rapid in the presence of oxygen. However, in contaminated sediments, oxygen levels are typically too low to sustain the rapid and complete biodegradation of buried hydrocarbons. Here, we explored the possibility to electrochemically manipulate the redox potential of a crude oil-contaminated marine sediment in order to establish, in situ, conditions that are conducive to contaminants biodegradation by autochthonous microbial communities. The proposed approach is based on the exploitation of low-voltage (2V) seawater electrolysis to drive oxygen generation (while minimizing chlorine evolution) on Dimensionally Stable Anodes (DSA) placed within the contaminated sediment. Results, based on a laboratory scale setup with chronically polluted sediments spiked with crude oil, showed an increased redox potential and a decreased pH in the vicinity of the anode of 'electrified' treatments, consistent with the occurrence of oxygen generation. Accordingly, hydrocarbons biodegradation was substantially accelerated (up to 3-times) compared to 'non-electrified' controls, while sulfate reduction was severely inhibited. Intermittent application of electrolysis proved to be an effective strategy to minimize the energy requirements of the process, without adversely affecting degradation performance. Taken as a whole, this study suggests that electrolysis-driven bioremediation could be a sustainable technology for the management of contaminated sediments.

The "Oil-Spill Snorkel": an innovative bioelectrochemical approach to accelerate hydrocarbons biodegradation in marine sediments.

This study presents the proof-of-concept of the "Oil-Spill Snorkel": a novel bioelectrochemical approach to stimulate the oxidative biodegradation of petroleum hydrocarbons in sediments. The "Oil-Spill Snorkel" consists of a single conductive material (the snorkel) positioned suitably to create an electrochemical connection between the anoxic zone (the contaminated sediment) and the oxic zone (the overlying O2-containing water). The segment of the electrode buried within the sediment plays a role of anode, accepting electrons deriving from the oxidation of contaminants. Electrons flow through the snorkel up to the part exposed to the aerobic environment (the cathode), where they reduce oxygen to form water. Here we report the results of lab-scale microcosms setup with marine sediments and spiked with crude oil. Microcosms containing one or three graphite snorkels and controls (snorkel-free and autoclaved) were monitored for over 400 days. Collectively, the results of this study confirmed that the snorkels accelerate oxidative reactions taking place within the sediment, as documented by a significant 1.7-fold increase (p = 0.023, two-tailed t-test) in the cumulative oxygen uptake and 1.4-fold increase (p = 0.040) in the cumulative CO2 evolution in the microcosms containing three snorkels compared to snorkel-free controls. Accordingly, the initial rate of total petroleum hydrocarbons (TPH) degradation was also substantially enhanced. Indeed, while after 200 days of incubation a negligible degradation of TPH was noticed in snorkel-free controls, a significant reduction of 12 ± 1% (p = 0.004) and 21 ± 1% (p = 0.001) was observed in microcosms containing one and three snorkels, respectively. Although, the "Oil-Spill Snorkel" potentially represents a groundbreaking alternative to more expensive remediation options, further research efforts are needed to clarify factors and conditions affecting the snorkel-driven biodegradation processes and to identify suitable configurations for field applications.