Pulsed electric field based antifouling method for salinometers

Summary form only given. Salinity changes in seawater are important for understanding 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, which are used for the measurement,are subject to biological growth (biofouling). Accurate measurements require frequent and careful cleaning of the sensors. In order to suppress biological growth at the sensors, an electrical sterilization method is being studied. 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 15 s at electric fields of 6 kV/cm. For an electrode gap of 2.5 cm this required voltages of 15 kV, generated by means of a Blumlein pulser with a thyratron as switch. Since the salinometer requires only a low flow rate, the intake in this system can be reduced from centimeter to millimeter size, and consequently allowed us to reduce the required voltage for biofouling prevention considerably. This in turn allowed us to replace the gas switch in the pulse gene tor by 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, the seawater between the electrodes, is approximately 5 Ohms. The repetition rate was set at 400 Hz. This allows us to apply at least two voltage pulses to every volume element of water entering the salinometer. The system is being tested in the Virginia Marine Science Museum in Virginia Beach, Va.