tional microbiocide program. This six-month trial began in the spring and continued throughout the summer and fall
cooling season. The goal was to achieve
performance at least equivalent to that
of conventional chemical treatment while
reducing the number of chemicals applied
to the cooling water and decreasing the
This institution’s 20-year-old plant
included a cooling system with three
cross-flow galvanized cooling towers containing high-efficiency film fill with three
1,000-ton centrifugal chillers and a stainless steel (grade 304) plate-and-frame
heat exchanger having a 400-ton capacity.
The condenser tubes had been replaced
the previous year with enhanced tubes.
Prior to the application of SONOXIDE
treatment, the system was operated at
five cycles of concentration and utilized
an all-organic phosphonate corrosion
and deposit control additive, an organic
dispersant with supplemental azole and
continuous brominating to 0.2 ppm to
0.4 ppm as free available chlorine. The
oxidizing biocide was supplemented with
a non-oxidizer, glutaraldehyde, at a dosage
rate of 45 ppm slug feed once per week.
Glutaraldehyde was included in the program to aid in biofilm control.
Upon trial startup, the water treatment program consisted only of low-power, high-frequency ultrasound for
microbiological control and one advanced
chemical cooling water treatment product with inherent biodegradable properties for deposit and corrosion control. No
cooling water pH control was exercised.
A sidestream coupon rack was installed
and included carbon steel and copper
corrosion coupons for the evaluation of
corrosion rates, as well as a biofilm
coupon for the determination of surface
Routine evaluation of total bacteria
levels was performed using industry-standard microbiological assay slides. As
shown in figure 1, ultrasonic treatment
maintained consistent control of total
bacteria in the acceptable range of 102 to
103 colony-forming units per milliliter
In addition to conducting visual
inspections, researchers assessed biofilm
Figure 1. Total Bacteria Counts Using Ultrasonic Treatment in University Trial.
Courtesy Ashland Specialty Chemical.
control through the use of a biofilm
coupon. Total system biofilm control was
achieved. The biofilm coupon revealed
no slime or biological fouling present
Surface biofilm control was further
evaluated upon chiller inspection. A
video probe inspection revealed clean,
‘like-new’ appearance of brushed, air-
Courtesy Ashland Specialty
This biofilm coupon, removed from the sidestream
coupon rack during a university trial of the ultrasound system, shows no evidence of slime or bio-fouling.
blown tubes in the first and second pass
with no indication of pitting or under-deposit corrosion.
Analytical evaluation of corro-
sion coupons revealed excellent
corrosion rates with no evidence
of localized corrosion.
Analytical evaluation of corrosion
coupons revealed excellent corrosion
rates with no evidence of localized corrosion. The 65-day corrosion rate was 0.262
mpy (mils per year, where mil equals
0.001 inch) for mild steel and 0.004 mpy
for copper. If oxidative microbiocides
had been present, it is anticipated that
corrosion rates would have been higher
and, therefore, the demand for corrosion
In this university trial, the ultrasonic
treatment achieved the study’s objectives
by reducing the total number of chemicals applied to the cooling system while
achieving effective microbiological control. The ultrasonic device operated con-
Cooling system performance
was optimized by eliminating
insulating biofilm on heat
tinuously without the need for routine
maintenance or operator interaction. In
addition, the treatment eliminated the
need for halogen testing and maintenance
of microbiocide feed and control systems.
Equally important, cooling system
performance was optimized by eliminating
insulating biofilm on heat transfer surfaces. Improvements in corrosion rates
were noted and attributed to eliminating
oxidant-induced corrosion commonly
experienced when applying such biocides.
This case study illustrates that the
application of ultrasonic treatment is an
excellent alternative to chemical micro-