Does a thicker SRB biofilm mean faster MIC pitting?
If a mathematical model directly relates the flux of sulfate entering the biofilm to MIC pitting rate, a thick SRB biofilm will mean more digestion of sulfate by SRB and thus faster pitting rate. Unfortunately, this is inconsistent with biofilm catalyzed electrochemical kinetics. A thicker SRB biofilm may help protect the biofilm community, but it does not necessarily promotes sulfate reduction at the iron surface. A thicker biofilm actually presents a thicker mass transfer barrier for sulfate diffusion. It also consumes more sulfate for biofilm maintenance. Both will lead to a smaller pitting rate. Remember, electrons from the iron dissolution reaction can only reach the SRB cells very close to the iron surface. Cells are very poor electron conductors! When SRB cells cannot receive the electrons from iron dissolution, they will use lactate as electron donor. This redox reaction is not electrodic, thus does not lead to electrochemical corrosion!
