Bio®lms of Leptothrix discophora SP-6, grown on 316L stainless steel (SS), ennobled the open circuit potential to 410 mV SCE. X-ray Photoelectron Spectroscopy (XPS) identi®ed MnO 2 within these bio®lms. Field exposed SS showed similar ennoblement after 30 days. XPS analysis of these samples revealed a mixture of dierent manganese minerals. Electrochemical reduction of MnO 2 was studied using electroplated SS. Plated MnO 2 was reduced amperometrically. The process was interrupted at dierent reduction stages. XPS analysis of remaining oxides showed that MnO 2 was reduced through MnOOH to Mn 2+. We conclude that biomineralized MnO 2 may increase corrosion rates by serving as a cathodic reactant.

Today, microbial drinking water quality is monitored through either time-consuming laboratory methods or indirect on-line measurements. Results are thus either delayed or insufficient to support proactive action. A novel, optical, on-line bacteria sensor with a 10-minute time resolution has been developed. The sensor is based on 3D image recognition, and the obtained pictures are analyzed with algorithms considering 59 quantified image parameters. The sensor counts individual suspended particles and classifies them as either bacteria or abiotic particles. The technology is capable of distinguishing and quantifying bacteria and particles in pure and mixed suspensions, and the quantification correlates with total bacterial counts. Several field applications have demonstrated that the technology can monitor changes in the concentration of bacteria, and is thus well suited for rapid detection of critical conditions such as pollution events in drinking water.

The noble shift in open-circuit potential exhibited by microbially colonized stainless steel (ennoblement) was investigated by examining the relationship among surface colonization, manganese deposition, and opencircuit potential for stainless steel coupons exposed to batch cultures of the manganese-depositing bacterium Leptothrix discophora. Open-circuit potential shifted from ؊100 to ؉330 mV SCE as a biofilm containing 75 nmol of MnO x cm ؊2 formed on the coupon surface but changed little further with continued MnO x deposition up to 270 nmol cm ؊2. Increased open-circuit potential corresponded to decreasing Mn(II) concentration in solution and to increased MnO x accumulation and attached cell density on the coupon surfaces. MnO x deposition was attributable to biological activity, and Mn(II) was observed to enhance cell attachment. The experimental results support a mechanism of ennoblement in which open-circuit potential is fixed near ؉350 mV SCE by the cathodic activity of biomineralized MnO x .

Culture-independent investigations of the bacterial diversity and activity in district heating systems with and without corrosion did not make it possible to relate one group of microorganisms with the observed corrosion. Fluorescence in situ hybridization by oligonucleotide probes revealed the dominance of beta-proteobacteria, sulphate reducing prokaryotes and alpha-proteobacteria. Analysis of a clone library from one Danish heating (DH) system showed that the most sequences formed two clusters within the alpha-proteobacteria affiliated to the families Rhizobiaceae and Acetobacteraceae and two clusters within the beta-proteobacteria belonging to the family Comamonadaceae. Functional groups were determined by microautoradiography showing aerobic and anaerobic bacteria (sulphate reducing and methanogenic bacteria). The corrosion study showed that pitting corrosion rates were five to ten times higher than the general corrosion rates, suggesting the presence of biocorrosion. The results indicate that several bacterial groups could be involved in corrosion of DH system piping including sulphate reducing prokaryotes, Acidovorax (within the beta-proteobacteria), methanogenic bacteria and others.