METHOD AND APPARATUS FOR KILLING MICROORGANISMS IN SHIP BALLAST WATER

摘要

PURPOSE: A method and apparatus for treating ship ballast water is provided to kill potentially undesirable aerobic and/or anaerobic microorganisms in the water to prevent them from being transported from one coastal area to another. CONSTITUTION: A method and apparatus for treating ship ballast water before it is discharged into coastal waters. The ballast water may contain harmful non-indigenous microorganisms. Before discharge, the ballast water is oxygenated and deoxygenated to reduce the populations of anaerobic and aerobic microorganisms, respectively. If anaerobic microorganisms are of no concern, the oxygenation step can be eliminated.. From the mixing tank 26, the oxygenated ballast water flow is further pumped into a vacuum chamber 34 where it is agitated for a suitable period by means of an internal agitator 36. The vacuum chamber 34 has sufficient space above the water level therein so that dissolved oxygen (DO) liberated from the water is released into this space from which it is easily removed by a vacuum pump 38 and then discharged to the atmosphere 40. The vacuum pump maintains a vacuum over the water within the chamber. ("Vacuum" is herein used to mean a pressure less than atmospheric pressure but greater than zero pressure.) The agitator 36 may be replaced by a Weir-type system 42 (FIG. 4) in which a series of vertical plates are placed in such a manner that they form a line of plates that are ever decreasingly shorter from the in-flow 27 to the out-flow 45 of the chamber 34; such a system creates a series of waterfalls which agitate the water sufficiently to release the dissolved oxygen into the vacuum that is maintained in the chamber. Any agitation system that liberates the DO for removal by the vacuum pump is acceptable.