No 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.

The most frequent way to survey green waste composts is to monitor the temperature during the composting process. However, if the temperature is a good index for global biological processes, it is not for the chemical stability. In order to identify a reliable index, this work investigates water extraction coupled to spectroscopic indexes such as E 2 /E 3 , E 4 /E 6 and SUVA 254 ratios, and fluorescence indexes such as Kalbitz, Milori, CP/PARAFAC and Fluorescence Region Integration. The measurements of these indexes are carried out with six samples from different sites with different green waste material composition. The results show that most indexes depend on the green waste origin more than the composting time; some depend mostly on the material origin while others on compost age. A comparison of these results indicates that the biochemical process occurs more rapidly than expected by the compost producers. The combination of these indicators gives useful information on the processes that take place during composting.