Influence of oxygen supply on heptadecane mineralization by Pseudomonas nautica

Sulphide production and corrosion in seawaters during exposure to FAME diesel

Experiments were designed to evaluate the corrosion-related consequences of storing/transporting fatty acid methyl ester (FAME) alternative diesel fuel in contact with natural seawater. Coastal Key West, FL (KW), and Persian Gulf (PG) seawaters, representing an oligotrophic and a more organic- and inorganic mineral-rich environment, respectively, were used in 60 day incubations with unprotected carbon steel. The original microflora of the two seawaters were similar with respect to major taxonomic groups but with markedly different species. After exposure to FAME diesel, the microflora of the waters changed substantially, with Clostridiales (Firmicutes) becoming dominant in both. Despite low numbers of sulphate-reducing bacteria in the original waters and after FAME diesel exposure, sulphide levels and corrosion increased markedly due to microbial sulphide production. Corrosion morphology was in the form of isolated pits surrounded by an intact, passive surface with the deepest pits associated with the fuel/seawater interface in the KW exposure. In the presence of FAME diesel, the highest corrosion rates measured by linear polarization occurred in the KW exposure correlating with significantly higher concentrations of sulphur and chlorine (presumed sulphide and chloride, respectively) in the corrosion products.

Biodegradation of sodium benzoate by a Gram-negative consortium in a laboratory-scale fluidized bed bioreactor

Gram-negative bacteria with the potential to metabolize n-alkanes and cyclic hydrocarbons were isolated from local soils and identified using 16S rDNA sequence analysis. Three isolates (CS1CO, GL1CO, GCI1CO) were identified as strains of Pseudomonas (P.) aeruginosa and a further strain (DSS2) as P. putida. Isolates were co-cultured in a laboratory-scale fluidized bed biofilm bioreactor (FBBR) utilizing sodium benzoate as the sole carbon source, under two batch and/or one continuous growth conditions. Biofilm and planktonic bacterial growth dynamics were monitored by plate counts, and optical density measurements (230 nm) determined benzoate biodegradation. Overall higher attached and planktonic bacterial counts, and benzoate depletion, were determined under batch compared to continuous conditions, and the bioreactor performed better during the second batch phase when compared to the first batch phase. It thus appeared that both the planktonic and biofilm components of the system were necessary for the most successful sodium benzoate degradation in this system.