Selective microbial enrichment by thermal treatments controls brass corrosion in methanation environments

This study investigates the effect of thermal treatments applied to a methanation inoculum on microbial community composition, surface morphology, and microbially induced corrosion of duplex brass (OT60, 40 wt% Zn), compared with sterile and untreated conditions. The treatments included: i) boiling for 120 min; ii) double autoclaving at 121 °C for 20 min; and iii) extended autoclaving at 121 °C for 60 min combined with 0.22 µm filtration and UV irradiation (sterile control). Electrochemical, chemical, and microbiological analyses were carried out to evaluate microbial modification and corrosion behavior during a 15-day exposure at 45 °C. Each treatment generated distinct microbial fingerprints, resulting in markedly different corrosion responses. Electrochemical impedance spectroscopy showed that the autoclaved condition exhibited the highest total resistance (42 kΩ·cm2 after 15 days), followed by the sterile (14 kΩ·cm2), boiled (6.5 kΩ·cm2), and biotic (3.8 kΩ·cm2) conditions. The autoclaved system was dominated by a biofilm enriched in spore-forming Bacilli (e.g., Caldalkalibacillus, Brevibacillus, Effusibacillus), which promoted the formation of a protective Cu2O/CuO-CaCO3 bilayer and limited metal release (Cu/Zn ratio: 0.79). In contrast, the both biotic and boiled systems, which biofilms were dominated by thermophilic genus Tepidiphilus, developed intermediate, less protective, Cu-Zn phosphate surface layers. The sterile condition exhibited purely chemical corrosion, characterized by direct alloy dissolution (Cu = 5.8 ppm; Cu/Zn ratio: 7.25) and the formation of fragile, non-protective oxide and phosphate deposits. Overall, thermal treatments alone were insufficient for complete sterilization, while selective microbial enrichment through autoclaving effectively mitigated brass corrosion via biogenic carbonate precipitation.