aquatic nuisance species in ship &# 39 ; s ballast water are killed by permeating to equilibrium a gaseous mixture consisting essentially of , preferably , ≧ 84 % nitrogen , ≧ 11 % carbon dioxide and ≦ 4 % oxygen through ship &# 39 ; s ballast water until the ballast water itself becomes hypercapnic to ≧ 20 ppm carbon dioxide , and , by association , acidic to ph ≦ 7 , while preferably further , and also , being rendered hypoxic to ≦ 1 ppm oxygen . the permeating is preferably realized by bubbling the gaseous mixture preferably obtained from an inert gas generator through the ballast water over the course of 2 + days while the ballast water is continually maintained a pressure less than atmosphere , preferably − 2 p . s . i . or less . the hypercapnic , acidic and hypoxic conditions — each of which can be independently realized — synergistically cooperate to kill a broad range of ans in the ballast water without deleterious effect on the environment when , and if , the ballast water in which the balance of dissolved gases has been changed is discharged .