Biocidal Effect of Cathodic Protection on Bacterial
Viability in Biofilm Attached to Carbon Steel
Kazuhiko Miyanaga, Ryosuke Terashi, Hirofumi Kawai, Hajime Unno, Yasunori Tanji
Department of Bioengineering, Tokyo Institute of Technology 4259 J2-15 Nagatsuta-cho,
Midori-ku, Yokohama 226-8501, Japan; telephone: þ81-45-924-5764; fax: þ81-45-924-5818;
Received 23 August 2006; accepted 8 November 2006
Published online 12 December 2006 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/bit.21278
ABSTRACT: Biofilm formed on carbon steel by various
species of bacterial cells causes serious problems such as
corrosion of steel, choking of flow in the pipe, deterioration
of the heat-transfer efficiency, and so on. Cathodic protec-
tion is known to be a reliable method for protecting carbon
steel from corrosion. However, the initial attachment of
bacteria to the surface and the effects of cathodic protection
on bacterial viability in the biofilm have not been clarified.
In this study, cathodic protection was applied to an artificial
biofilm containing Pseudomonas aeruginosa (PAO1), a bio-
filmconstituent, on carbonsteel. The aimsof thisstudywere
to evaluate the inhibition effect of cathodic protection on
biofilm formation and to reveal the inhibition mechanisms.
The viability of PAO1 in artificial biofilm of 5 mm thickness
on cathodically protected steel decreased to 1% of the initial
cell concentration. Analysis of pH distribution in the arti-
ficial biofilm by pH microelectrode revealed that pH in
proximity to carbon steel increased to approximately 11
the artificial biofilm was under the pH conditions of over
experimental values. These results indicate cells in the
artificial biofilm were killed or damaged by cathodic protec-
tion due to pH increase.
Biotechnol. Bioeng. 2007;97: 850–857.
? 2006 Wiley Periodicals, Inc.
KEYWORDS: biofilm; cathodic protection; pH increase;
carbon steel; bacterial viability
In various industrial fields, biofilm formation on carbon
steel causes many problems such as choking of the pipe,
deterioration of heat-transfer efficiency, microbiologically
influenced corrosion (MIC), and so on (Coetser and Cloete,
2005; Videla and Herrera, 2005). Especially, the amount of
loss induced by corrosion of metals such as carbon steel is
estimated as a serious problem (Graves and Sullivan, 1996).
MIC has been considered to occur as a consequence of some
factors, oxygen concentration gradients on the carbon steel
surface caused by heterogeneous biofilm formation (Little
et al., 1997; Tanji et al., 1999), hydrogen consumption by
sulfate reducing bacteria in the biofilm (Bryant et al., 1991;
Neria-Gonza ´lez et al., 2006), manganese oxide reduction
mechanisms (Dexter et al., 2003; Shi et al., 2002), and so on.
Therefore, countermeasures against biofilm formation are
One alternative method for control of biofilm formation
is use of bactericidal reagent such as oxidative or non-
oxidative biocide. In the real environment, however, the
short-lived effect of biocide and/or the appearance of
resistant bacteria against biocide are serious problems. In
addition, the biocide cannot affect the mature biofilm
because of the difficulty of biocide diffusion into the thick
biofilm. Besides biocide, surface coating of substrate or
material alloyed with antibacterial silver has been improved.
However, they are all costly measures. Meanwhile, cathodic
protection is well known as an effective electrochemical
and Chadwick, 1994; Schwerdtfeger and McDorman, 1952).
There are two basic types of cathodic protection; galvanic
anode system and impressed current system. The galvanic
anode method is the way to apply the protective current to
the target material connected to the low-potential galvanic
anode. This simple method cannot be applied to the
environment where the material is seriously corroded due to
the low durability of the galvanic anode. On the other hand,
the impressed current method is the way to apply the
protective currentfrom the direct-current power supply and
can be used as a corrosion protection for a long term.
Hitherto, there have been some reports about the effects of
Correspondence to: Y. Tanji
Contract grant sponsor: This research was financially supported from the Japanese
Ministry of Education, Culture, Sports, Science and Technology
Contract grant number: 16760629
Biotechnology and Bioengineering, Vol. 97, No. 4, July 1, 2007
? 2006 Wiley Periodicals, Inc.
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Miyanaga et al.: Biocidal Effect of Cathodic Protection in Biofilm
Biotechnology and Bioengineering. DOI 10.1002/bit