Abstract
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.
Highlights
Petroleum hydrocarbons are released into the marine environment both from natural seeps and from anthropogenic activities involved in the drilling, manufacturing, storing, and transporting of crude oil and oil products (Gong et al, 2014).Application of oil dispersants has been a critical response measure to mitigate impacts of marine oil spill for decades (Prince, 2015)
Since the graphite rods do not alter the physical–chemical properties of the water–sediment interface and are not expected to modify the rate of oxygen transport from the headspace to the sediment, the observed enhancement of oxygen consumption was likely driven by the electrons released to the graphite rods which reacted with oxygen forming water as a byproduct
This study presented the proof of concept of the “Oil-Spill Snorkel,” a novel bioelectrochemical approach to accelerate in situ the biodegradation of petroleum hydrocarbons in anoxic marine sediments
Summary
Petroleum hydrocarbons are released into the marine environment both from natural seeps and from anthropogenic activities involved in the drilling, manufacturing, storing, and transporting of crude oil and oil products (Gong et al, 2014).Application of oil dispersants has been a critical response measure to mitigate impacts of marine oil spill for decades (Prince, 2015). Once the dispersed oil reaches the sediments it tends to persist there for a very long time due to the prevailing anoxic conditions which drastically limit the occurrence of oxidative biodegradation processes. Both physical–chemical and biological treatment methods (i.e., bioremediation) have been proposed for the cleanup of oil polluted sediments, with the latter receiving a greater attention due to the lower costs, lower environmental impact, and wide applicability to a range of contamination scenarios (Fodelianakis et al, 2015). The interplay between the (bio)availability of electron acceptors (e.g., oxygen, sulfate, nitrate) and hydrocarbons, as the electron donors and carbon sources for microorganisms, is certainly one of the most important factors influencing the performance of sediment bioremediation systems (Lu et al, 2014a)
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