Bacillus bioaugmentation with a suspended PET carrier shows more persistent corrosion protection of Q235B steel in industrial cooling water.

Maintaining microbial corrosion protection in industrial cooling water is difficult because water chemistry changes during operation and introduced bacteria must coexist with indigenous microorganisms. A 28-d rotating coupon experiment was conducted using actual makeup water from a coal-fired power plant. Four treatments were compared: untreated water (R0), carrier only (R1), a 1:1 mixture of Bacillus cereus BC3 and Bacillus subtilis BS2 without a carrier (R2), and the same inoculum with a suspended PET carrier (R3). R2 and R3 were inoculated once at day 0. R1 did not significantly reduce the day-28 corrosion rate relative to R0. R2 showed a larger early increase in interfacial resistance, whereas R3 maintained higher charge transfer resistance and film resistance during the middle and later stages. At day 28, corrosion inhibition efficiencies were 44.51% for R2 and 60.67% for R3. The relative abundance of Bacillus on the steel declined more slowly in R3. At the endpoint, R3 had a more continuous surface layer, higher surface Ca, stronger carbonate signals, and higher urease and carbonic anhydrase activities. Metagenomic and metabolomic profiles further distinguished R3 from R2. The corrosion rate of R3 was similar in magnitude to the plant monitoring value under the routine low-phosphorus treatment program, although the operating conditions differed. A scenario analysis based on plant operating data further indicated the potential to reduce external phosphorus input by lowering reliance on the existing phosphorus-containing corrosion inhibitor.