title: Does phosphate enhance the natural attenuation of crude oil in groundwater under defined redox conditions?
abstract: After a crude oil spill caused by a broken pipeline in 2009 to a gravel aquifer in southern France, degradation processes under various redox conditions progressively established, but at rates that predict a long life-time of the source under natural attenuation after partial source removal. In this study, we aimed at identifying the rate-limiting factors for each redox condition, with special emphasis on phosphate as limiting nutrient. The study was conducted in laboratory microcosms assembled with material collected on site: sediments, water from monitoring wells, oil and microbial sludge. Redox conditions were promoted by adding electron acceptors (either oxygen, nitrate, limonite (FeO(OH)), cryptomelane (K(Mn(4+),Mn(2+))8O16), or sulfate). For each condition, the role of phosphate was studied by repeated additions for up to 290days. The results showed a very strong stimulation of aerobic and denitrifying rates of oil degradation by phosphate, provided that oxygen and nitrate were repeatedly supplied. Phosphate caused also a marked stimulation of methanogenic degradation, and a relatively small stimulation of metal reduction. These anaerobic processes started only after marked lag phases, and phosphate shortened the lag phase for methanogenic degradation. Degradation of aromatic and aliphatic hydrocarbons with less than 8 carbons, including benzene, was confirmed even under unstimulated conditions. It is concluded that degradation rates at the site are limited by both, availability of electron acceptors and availability of phosphate needed for promoting microbial growth.
authors.affiliation: Aix-Marseille Université-CNRS, Laboratoire Chimie Environnement, FRE 3416 Marseille, France; French Environment and Energy Management Agency, 20 avenue de Grésillé-BP 90406 Angers Cedex 01, France.
authors.forename: Violaine
authors.initials: V
authors.lastname: Ponsin
authors.affiliation: Aix-Marseille Université-CNRS, Laboratoire Chimie Environnement, FRE 3416 Marseille, France.
authors.forename: Olsen Raïnness
authors.initials: OR
authors.lastname: Mouloubou
authors.affiliation: Aix-Marseille Université-CNRS, Laboratoire Chimie Environnement, FRE 3416 Marseille, France.
authors.forename: Pascale
authors.initials: P
authors.lastname: Prudent
authors.affiliation: Aix-Marseille Université-CNRS, Laboratoire Chimie Environnement, FRE 3416 Marseille, France. Electronic address: patrick.hohener@univ-amu.fr.
authors.forename: Patrick
authors.initials: P
authors.lastname: Höhener
mesh_terms: D001673:Biodegradation, Environmental / Q000187:drug effects; D005602:France; D019015:Geologic Sediments; D060587:Groundwater / Q000737:chemistry* / Q000382:microbiology; D006841:Hydrocarbons, Aromatic; D010084:Oxidation-Reduction; D010578:Petroleum / Q000032:analysis / Q000378:metabolism*; D059392:Petroleum Pollution; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism*
chemical_list: D006841:Hydrocarbons, Aromatic; D010578:Petroleum; D010710:Phosphates; D014874:Water Pollutants, Chemical
keywords: Aquifer; Enhancement; Hydrocarbons; La Crau nature reserve; Microcosms; Nutrients