Corrosion of Cu by a sulfate reducing bacterium in anaerobic vials with different headspace volumes

Microbiologically influenced corrosion (MIC) of copper by Desulfovibrio vulgaris, a sulfate reducing bacterium (SRB), was investigated in anaerobic vials with a fixed broth volume of 40 mL but varied headspace volumes (10 mL, 85 mL 160 mL). It was found that the headspace volume variation had a very large effect on the dissolved [H₂S] in the broth and the cell counts of planktonic and sessile cells, as well as Cu corrosion severity. A 16× smaller headspace led to a 1.6-fold increase in the dissolved [H₂S], a 13-fold decrease in sessile SRB cell count, a 32-fold decrease in planktonic cell count and a 3.7-fold increase of Cu weight loss. SEM images revealed that different headspace volumes caused different corrosion patterns on the immersed coupons. With a lower headspace volume, pitting corrosion was observed, while with a higher headspace volume, intergranular corrosion was seen. The results confirmed that SRB MIC of Cu belongs to metabolite-MIC (M-MIC) by H₂S, unlike SRB MIC of carbon steel that belongs to extracellular electron transfer-MIC (EET-MIC) that is directly correlated with sessile cell counts rather than dissolved [H₂S]. .