CLOSED LOOP CONTROL OF BOTH PRESSURE AND CONTENT OF BALLAST TANK GASES TO AT DIFFERENT TIMES KILL BOTH AEROBIC AND ANAEROBIC ORGANISMS WITHIN BALLAST WATER

摘要

The ullage space gases (11) of a ship's ballast tanks 1 (i) are de-pressurized to a pressure less than atmosphere -- called an 'underpressurized' condition -- of most preferably about 14.7 PSIA or lower, simultaneously that (ii) they are inerted, preferably to < 4% 02 and more preferably to < 2% 02. Oxygen within the ballast water (12) is rapidly, preferably within hours, substantially depleted, preferably to < 1% PPM and more preferably to < .6 PPM, by circulating these inerted ullage space gases (11) through the ballast water (12) as bubbles from bubbling nozzles (13), removing oxygen from the ballast water (12) more by outgassing than by diffusion. The rapidly de-oxygenated ballast water (12) is preferably so maintained for the substantial portion of the ship's voyage, which is effective in killing most aerobic aquatic life within the ballast water (12). The ballast tanks (1) may then be re-pressurized to atmosphere or above while oxygen­containing mixed gases, normally air, are bubbled through the ballast water (12), shocking and killing anaerobic aquatic life.