Microbial attack on subsea sprayed concrete

Paper in proceeding, 2016

A novel deterioration process has recently been discovered in several Norwegian subsea tunnels resulting in degradation of the sprayed concrete matrix and destructive corrosion of steel fibers in association with biofilms rich in Mn(IV), Fe(III) and exopolymers. Microbial processes together with abiotic attack from saline ground water, containing high concentrations of Cl−, SO42−, Mg2+ and HCO3 −, are assumed to be responsible for the degradation. In this initial study of the biofilm microbial communities, high throughput amplicon sequencing of 16S rRNA genes was used to survey the biofilm composition and diversity. Results showed a high abundance of iron oxidizing bacteria within Mariprofundus, which was in accordance with the observed accumulation of Fe(III) and exopolymers in the biofilms. Also iron and manganese reducing bacteria were detected. Surprisingly, the biofilm harbored autotrophic nitrogen converting microorganisms at high relative abundances, while no known manganese oxidizingor sulfur reducing bacteria were detected. Furthermore, a number of the numerically important contributors in the biofilm communities could not be assigned to any function. Apparently, the biofilm transformations were more complex than initially anticipated and the role of for instance the nitrogen converting- and the undetermined bacteria for the degradation processes remains unsolved.