Pulsed electric field based antifouling method for salinometers

The measurement of salinity in seawater is important for the understanding of global atmospheric and oceanic dynamics and their associated climate changes. Measurements of the electrical conductivity allow us to determine the salinity. Unfortunately, the electrical sensors, used for this measurement, are subject to biological growth (biofouling). Accurate measurements require frequent and careful cleaning. In order to suppress biological growth at the sensors, an electrical sterilization method is being explored. It is based on the application of pulsed electric fields to the water at the intake of the sensor. This method has been successfully tested in the laboratory as well as in field experiments. The optimum pulse duration for biofouling prevention was found to be approximately 1/spl mu/s at electric fields of 6 kV/cm. For an electrode gap of 2.5 cm this requires a voltage of 15 kV, which was generated by means of a Blumlein pulser with a thyratron as switch. Since the salinometer requires only a low flow rate, the dimensions of the intake of this system could be reduced from centimeter to millimeter size. This allowed us to reduce the required voltage for biofouling prevention considerably and to replace the plasma switch in the pulse generator by an array of semiconductor switches (MOSFETs). The voltage pulse has a duration of 700 ns (rise time: 20 ns), and an amplitude of 1000 V, generating an electric field of 6.7 kV/cm in the 1.5 mm electrode gap. The impedance of the load, seawater between the electrodes, is approximately 5 /spl Omega/. The repetition rate was set at 400 Hz to allow us to apply at least two voltage pulses to every volume element of water entering the salinometer. The system was set up at the Virginia Marine Science Museum in Virginia Beach, VA, and was operated continuously for eight weeks. Whereas the control unit showed strong biocontamination, the treated unit had much less of biofouling.