It is now clear that the IMO 2004 Ballast Water Convention (aimed at preventing undesirable beasties and other things being transported across the world and given a new lease of life elsewhere) will enter into force on 8 September 2017, having achieved the necessary number of ratifications. It sets two standards for systems, D1 (exchange) and D2 (treatment). Essentially all newbuilds will have to have systems complying with D2 after 8 September. All existing vessels covered by the Convention will have to comply with D1 from that date, and with D2 from the date of the next IOPP certificate renewal. The UK government is said to be drawing up a scheme for deferral in deserving cases: but don’t hold your breath.
Details of the coming into force of the Convention here and here.