Materials Sciences and Applications, 2012, 3, 253-258
http://dx.doi.org/10.4236/msa.2012.34037 Published Online April 2012 (http://www.SciRP.org/journal/msa)
253
Microbiological Induced Corrosion on Brass in Recycling
Cooling Water System Makeup by Reclaimed Water*
Ping Xu1,2, Zhaoyi Xu1, Jin Wang1, Yajun Zhang2, Ting Liu2
1School of Civil Engineering and Architecture, Beijing Jiaotong University, Beijing, China; 2Key Laboratory of Urban Stormwater
System and Water Environment, Beijing University of Civil Engineering and Architecture, Ministry of Education, Beijing, China.
Received January 18th, 2012; revised February 27th, 2012; accepted March 29th, 2012
ABSTRACT
The impacts of microorganism on brass corrosion were studied in static experiment in this paper. Two main factors,
temperature and concentration ratio, were considered. According to the actual operation of recycling cooling water sys-
tem, four temperatures (15˚C, 25˚C, 35˚C and 45˚C) and four concentration ratios (1, 2.5, 3.5 and 4.5) were selected in
the experiment. Corrosion potential, current density, average corrosion rate were measured by time. The results showed
that: microorganism often aggravated corrosion of brass during initial and final stages, but alleviated its corrosion at the
middle time. With the extension of time that brass immersed in the solution, the microbes began to intensify the
corrosion of the metal. When concentration ratios were 2.5 and 3.5 and temperature was 15˚C, microbe promoted brass
corrosion obviously and corrosion degrees.
Keywords: Reclaimed Water; Brass; Microbiologically Induced Corrosion; Corrosion Potential; Corrosion Current
Density; Average Corrosion Ratio; Temperature; Concentration Ratio
1. Introduction
Almost every surface can be colonized by bacteria, form-
ing biofilms [1]. The corrosion due to existence or action
of the microorganisms in biofilm is called microbiologi-
cally-influenced corrosion (MIC). Many metals are sen-
sible to MIC. Pitting, crevice corrosion, hydrogen em-
brittlement and deposit corrosion caused by MIC almost
involve all kinds of fields, such as petrochemical industry,
aviation, shipping, powder industry and so on [2-6]. Ac-
cording to statistics, MIC accounted for 20% in metal
and building materials corrosion damages [7]. The direct
economic loss by MIC is about 300 to 500 billion dollars
[8].
Because of serious water shortage in some big cities in
China, such as Beijing, Tianjin, Dalian and so on, it is a
feasible method to reuse reclaimed water to cooling wa-
ter system of power plant. However, there are full of nu-
trients in reclaimed water and the temperature is high in
recycling cooling water system. These conditions are
beneficial to microorganisms growing on metal surfaces.
A variety of microorganisms and their metabolic reaction
products may promote the deterioration of the underlying
substratum. For ultimately biocorrosion control, it is
firstly needed to understand the impacts of microorgan-
ism on metal corrosion. Brass is widely used in con-
denser of cooling water system of power plants in China.
The impacts of microorganism on brass corrosion were
studied by electrochemical method and mass loss method
in this paper. Two main factors, temperature and concen-
tration ratio, were considered.
2. Materials and Method
2.1. Electrochemical Method
Shanghai Chen Hua CHI660C electrochemical work-
station was used for experiment. Its scanning speed was
0.01 V/s and the sensitivity was 10–4 A/V. Ag/(AgCl)/
KCl (0.1 mol/L) was selected as reference electrode and
platinum was as counter electrode.
During experiment, cross-sectional area of HSn70-1A
brass was 1 cm2. Its main chemical compositions was
shown as following (Wt%): Pb ≤ 0.05, Fe ≤ 0.10, Sb ≤
0.005, P ≤ 0.01, Bi ≤ 0.002, Sn 0.8 - 1.3, As 0.03 - 0.06,
Cu 69.0 - 71.0, Zn little.
*The paper is supported by two Chinese national grand projectsfor
water pollution control: Integrative Technology and Demonstration on
Reclaimed Water Utilized to Industry in Beijing (2009ZX07314-009-
04); Research Technology of and Demonstration on Urban Water
Conservation (2009ZX07317-005).
In electrochemical experiment, corrosion potential and
current density could be got by Tafel curves, which were
obtained by dynamic potential scanning method Corro-

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water
254
sion potential reflects corrosion tendency or degree and
corrosion current density shows corrosion rate. More
negative corrosion potential means that metal is more
vulnerable to corrosion. Higer current density reflects the
faster corrosion rate of metal.
2.2. Mass Loss Method
Type I (50 mm × 25 mm × 2 mm) HSn70-1A brass cou-
pons were selected for the experiment. Average corrosion
rate of a brass coupon could be calculated by the formula
as follows:

0
87600 mm
Xst


 (1)
where X-average brass corrosion rate, mm/a;
m-mass loss of a brass coupon in experiment, g;
m0-mass loss of a brass coupon in blank test, g;
s-surface area of a brass coupon, cm2;
ρ-density of a brass coupon, g·cm–3;
t-test time, h.
2.3. Reclaimed Water
Reclaimed water was obtained from a makeup pipe of a
cooling water system of a thermal power plant in Beijing.
Table 1 showed the quality of reclaimed water in the
experiment.
2.4. Experiment Arrangement
Two main factors, temperature and concentration ratio,
were considered in static experiment. According to the
actual operation of recycling cooling water system, four
temperatures (15˚C, 25˚C, 35˚C and 45˚C) and four con-
centration ratios (1, 2.5, 3.5 and 4.5) were selected in the
experiment. For obtaining microbial influences on brass
Table 1. Reclaimed water in a thermal power plant in Bei-
jing.
Item pH
Conductivity
us/cm
Total
hardness
mg/L
Alkalinity
mmol/L
Value 7.53 1134 248 3.2
Item Iron
ug/L
Turbidity
NTU
Cl–
mg/L
COD
mg/L
Value 157.9 9.1 111.3 5.0
Item TP
mg/L
NH4-N
mg/L
2
4
SO 
mg/L
SS
mg/L
Value 0.9 1.0 114.4 5
Item Total dissolved solids
mg/L
HPC
cfu/ml
Value 534 2 × 104
corrosion, experiments were operated in reclaimed water
with bacteria and reclaimed water without bacteria. Re-
claimed water with bacteria was directly obtained from
the make-up system of circulating cooling system of a
thermal power plant in Beijing. Reclaimed water without
bacteria could be got after disinfection in a high pressure
steam sterilizer with 121˚C ± 1˚C temperature for 20
minutes.
3. Results and Discussion
3.1. Microbiological Induced Corrosion on Brass
in Different Temperatures
3.1.1. Corrosion Po te ntial
Corrosion potentials in reclaimed water with or without
bacteria in different temperatures were shown in Figure
1.
According to Figure 1, corrosion potentials of brass in
15˚C reclaimed water with bacteria are more negative
than the values in bacteria free water from start to finish,
existence of microorganism worsened the corrosion ob-
viously. Under other temperatures, compared with re-
claimed water without bacteria, corrosion potentials in
one with bacteria were more negative at the beginning
and last time, but less negative at the middle stage. That
means that microorganism aggravated corrosion of brass
during initial and final stages, but alleviated the corrosion
tendency at the middle time. At the early time, biofilm
had not fully formed yet. Uneven covering layer resulted
more serious corrosion. With the growth of biofilm, more
uniform and deeper layer retarded the tendency of corro-
sion. At the same time, formation of biofilm hindered
corrosive ions from arriving at the surface of brass. Adult
biofilm had stable ecosystem. More serious corrosion
would be caused by metabolic reactions or deposition.
Moreover, compared with corrosion potentials in 15˚C,
25˚C, 45˚C, values in 35˚C were all most negative when-
ever in reclaimed water with bacteria or not.
3.1.2. Corrosion Curr ent Densit y
Corrosion current density in reclaimed water with or
without bacteria in different temperatures were shown in
Figure 2.
According to Figure 2, both in reclaimed water with or
without bacteria, current densities were also higher at
higher temperatures. That means corrosion rates of brass
in higher environment were faster than the values in
lower temperature.
Moreover, compared with current densities in 25˚C,
35˚C and 45˚C reclaimed water with bacteria or not, cur-
rent densities in one with bacteria were higher at the be-
ginning and last stages and lower at middle stage. The
lowest densities in reclaimed water with bacteria oc-
curred on the third or fifth day. Current densities in the

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water
255
Figure 1. Corrosion potentials in reclaimed water with or without bacteria in different temperatures. (a) 15˚C; (b) 25˚C; (c)
35˚C; (d) 45˚C.
Figure 2. Corrosion current density in reclaimed water with or without bacteria in different temperatures. (a) 15˚C; (b) 25˚C;
c) 35˚C; (d) 45˚C. (

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water
256
water with bacteria began to exceed the values in bacteria
free one after fifth day. In the initial stages of brass im-
mersed in reclaimed water, maybe on first day, the pres-
ence of microorganisms would accelerate the corrosion
rate. Then with the biofilm on the surface of brass mature
gradually, it prevented corrosion ions from contacting
with the metal, so corrosion rates decreased at these stages.
After that period, corrosion rates in reclaimed water be-
gan to increase and ultimately exacerbate corrosion rates
of brass. Maybe uneven biofilm on the surface caused
serious corrosion of the metal.
3.1.3. Average Corrosion Rate
Average corrosion rates of couples in reclaimed water
with or without bacteria in different temperatures were
shown in Figure 3.
According to Figure 3, the developments of average
corrosions in different temperatures were similar to the
results of electrochemical experiments. In 25˚C, 35˚C
and 45˚C reclaimed with bacteria, compared with aver-
age corrosions in bacteria free reclaimed water, at first
stage, often within one or two days, corrosions of brass
were higher. Then the corrosions began to decrease and
were lower than the values in bacteria free one. For a
long time, often more than 9 days, average corrosions in
reclaimed water with bacteria began to increase and ul-
timately were higher than values in bacteria free one.
Moreover, average corrosion rates in 35˚C and 45˚C
were higher than the rates in 15˚C and 25˚C. The faster
values occurred in 35˚C and the lowest one occurred in
15˚C. The results further proved that the corrosion of
brass would be effected by micro-organisms. For a long
time, corrosion rates in reclaimed water with bacteria
would be faster than ones in bacteria free reclaimed wa-
ter.
3.2. Microbiological Induced Corrosion on Brass
in Different Concentration Ratio
3.2.1. Corrosion Po te ntial
Corrosion potentials in reclaimed water with or without
bacteria in different concentration ratios were shown in
Figure 4.
Based on Figure 4, both in reclaimed water with or
without bacteria, corrosion potentials were more negative
at higher concentration ratios. That means increasing
concentration ratios would aggravate the corrosion ten-
dency of brass in reclaimed water. There were high con-
centrated ions and nutrient substances under higher ratios,
which were beneficial to corrosion development and
caused more serious corrosion.
In four ratios, corrosion potentials in reclaimed water
with bacteria were more negative than values in bacteria
free one when concentration ratios were 2.5 and 3.5.
Under these conditions, the roles of the microbe to pro-
mote corrosion were more obvious and corrosion de-
grees of brass in reclaimed water with bacteria were
more serious. When concentration ratios were 1 and 4.5,
corrosion potentials in reclaimed water with bacteria
were more positive than values in bacteria free one
within 10 days. After that, corrosion potentials in re-
claimed water with bacteria move to negative direction
and aggravated the brass corrosion.
3.2.2. Corrosion Curr ent Densit y
Corrosion current density in reclaimed water with or
without bacteria in different concentration ratios were
shown in Figure 5.
Based on Figure 5, both in reclaimed water with or
without bacteria, corrosion current densities were also
higher at higher concentration ratios. That means in-
creasing concentration ratios would faster the corrosion
of brass in reclaimed water. High concentrated ions and
nutrient substances promoted corrosion development and
caused more serious corrosion.
Compared with two curves of reclaimed water with
bacterial and without bacterial in Figure 5, corrosion
current densities of without bacterial one decreased with
the time growth, but corrosion current densities of with
bacterial one decreased at initial stage and then increased
at second stage. The lowest point occurred at fifth or
sixth day at ratio of 1 and 2.5. When concentration ratio
was up to 3.5 and 4.5, the lowest point had been put off,
often at 10th day. With the extension of time that brass
immersed in the solution, the microbes began to intensify
the corrosion of the metal.
4. Conclusions
In a conclusion, whenever in reclaimed water with bacte-
ria or not, most serious corrosion occurred at 35˚C and
increasing concentration ratios would aggravate the cor-
rosion tendency of brass.
Microorganism often aggravated corrosion of brass
during initial and final stages, but alleviated its corrosion
at the middle time. With the extension of time that brass
immersed in the solution, the microbes began to intensify
the corrosion of the metal. When concentration ratios
were 2.5 and 3.5 and temperature was 15˚C, microbe
promoted brass corrosion obviously and corrosion de-
grees in reclaimed water with bacteria were more serious.
5. Acknowledgements
The research was supported by two Chinese national
grand projects for water pollution control: Integrative
Technology and Demonstration on Reclaimed Water
Utilized to Industry in Beijing (2009ZX07314-009-04);
Research Technology of anDemonstration on Urban d

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water 257
Figure 3. Average corrosion rates of couples in reclaimed water with or without bacteria in different temperatures. (a) 15˚C;
(b) 25˚C; (c) 35˚C; (d) 45˚C.
Figure 4. Corrosion potentials in reclaimed water with or without bacteria in different concentration ratios. (a) Ratio-1; (b)
Ratio-2.5; (c) Ratio-3.5; (d) Ratio-4.5.

Microbiological Induced Corrosion on Brass in Recycling Cooling Water System Makeup by Reclaimed Water
258
Figure 5. Corrosion current density in reclaimed water with or without bacteria in different concentration ratios. (a) Ratio-1;
(b) Ratio-2.5; (c) Ratio-3.5; (d) Ratio-4.5.
Water-Conservation (2009ZX07317-005). Moreover, the
paper was also supported by Key Laboratory of Urban
Stormwater System and Water Environment of Beijing
University of Civil Engineering and Architecture of
Ministry of Education.
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