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·cm 2 after 15 days), followed by the sterile (14 kΩ·cm 2 ), boiled (6.5 kΩ·cm 2 ), and biotic (3.8 kΩ·cm 2 ) 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 Cu 2 O/CuO-CaCO 3 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.