Effects of various metal substrata on accumulation ofPseudomonas aeruginosabiofilms and the efficacy of monochloramine as a biocide

Monochloramine at 4 mg·l−1 was used to treat biofilms of Pseudomonas aeruginosa grown in annular reactors on various metal substrata, including stainless steel, mild steel and copper. Disinfection of in situ biofilms was most efficient on the stainless steel slides. The treatment reduced viable cells in the biofilm on the stainless steel slides by more than 4 orders of magnitude after 60 min, while the same treatment reduced viable cells in the biofilms on the other slides (mild steel and copper) by only 2 orders of magnitude. Mild steel corrosion products retarded the disinfection of homogenized biofilm cells. The composition of steady state biofilms on the various substrata (before biocide treatment) differed. Biofilm on stainless steel slides had more viable cells but less extracellular polymeric substance (EPS). Biofilms on mild steel and copper slides had fewer viable cells but more EPS. Almost 95% of total cells in the biofilm on the copper slides were dead cells. The lower efficacy of disinfection of in situ biofilms on mild steel and copper is hypothesized to be due to the higher EPS content of biofilms on those substrata.