Biological Control in Cooling Towers Treated with Pulsed-Power Systems

Biological control is the foundation of cooling tower water treatment. Biofilm can directly cause corrosion problems (microbial induced corrosion, MIC), pathogen concerns (Legionella), increased pump pressure, heat-transfer problems, dermatological effects, and malodors. With the increasing restrictions being imposed at the federal and state level regarding chemical use in cooling towers (CAA, CWA, OSHA, FIFRA), biological control has become much more difficult. A safe and effective alternative to current treatment methods is needed.

Pulsed-Power Technology in the Food Industry

Pulsed-power technology is an FDA-approved electronic process for the pasteurization of pumpable fluids. A recent FDA report (ref. 1) describes in detail the successes with these systems as a low energy method of pasteurization. Although there are only two commercially available systems for pasteurization, PurePulse (a spin-off of Maxwell Laboratories) and Thomson-CSF, many different processes have been successfully tested. These processes all involve a pulsed electric field delivered to the fluid at a high power level. Four different types of pulses have been tested, and all show efficacy as a biocide. The four pulse shapes are:

1. Exponential Decay
2. Square Wave
3. Bipolar
4. Oscillatory (Sine Wave)

The typical setup exposes the fluid to 5 to 30 pulses of an electric field at a strength of 30 kV/cm. This exposure will result in several log kills of a variety of bacteria and yield longer shelf life than standard heat pasteurization using less energy and having no effect on taste. In these examples of pasteurization, the fluid is passed between two electrodes, and 20 to 40m sec electric field pulses are applied. There are a variety of configurations to produce this field. Once above a threshold value, the duration of the pulse, the strength of the pulse, and the number of pulses directly influence the effectiveness of the treatment. The original Maxwell patent (ref. 2) uses an induced electric field generated by a coil. For pasteurization this type of field is not optimal, since the electric field is not uniform over the cross-section of the pipe and actually goes to zero at the center of the pipe.

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