Disinfecting Marine Vessel Ballast Water with UV

To assist operators of cruise ships, tankers, semi-submersibles, jack-up rigs and other large ocean-going vessels to meet the International Maritime Organisation’s (IMO’s) ballast water discharge requirements, UV disinfection specialist Hanovia has partnered with three of the world’s leading systems integrators to provide validated, on-board water treatment systems that are easy to install and use.

All ocean-going vessels take on water to provide ballast and stability. It is usually taken on in coastal port areas and transported to the next port of call – sometimes on the other side of the world – where it may be discharged. Much of this water contains marine microorganisms such as zooplankton, algae, bacteria and the eggs, cysts and larvae of various species. While many die in transit, some survive and invade the local marine environment, out-competing native species and causing serious damage to native ecosystems. Environmental damage caused by ballast water is now regarded as one of the greatest threats to the world’s oceans.

Two methods have been proposed to combat this problem: onboard ballast water treatment and ballast water exchange. As the name suggests, ballast water treatment involves treatment of ballast water prior to discharge, while ballast water exchange involves ballasting and de-ballasting in the open ocean before coming into ports and coastal waters. This open ocean exchange is not an ideal solution as it is potentially unsafe and can destabilise the vessel. Also, because existing ballast water exchange systems do not completely drain the tanks, sediment and a residual amount of water can remain, leaving behind non-indigenous species which could be discharged in port later.

As well as being unsafe, open ocean ballast water exchange is difficult to regulate and to monitor, so many operators simply do not do it. Because of this the IMO is setting much tougher standards to control ballast water practices and has published two Conventions to tackle the problem. The first is the International Convention for the Prevention of Pollution from Ships (MARPOL), dealing with waste and sewage discharge from ships (ratified in 2003), and the second is the Ballast Water Management (BWM) Convention, to control the spread of alien species (due for ratification in 2009). Under the BWM Convention, vessels will have to treat all ballast water so that discharges contain less than 10 viable organisms per cubic metre equal to or greater in size than 50 µm in size.

To help operators confront these requirements Hanovia, in tandem with the leading systems integrators, has devised a UV disinfection system that, in conjunction with a filter, kills or removes virtually all microorganisms present in ballast water. The combined system comprises a high intensity, medium pressure UV disinfection unit and an automatic back-flush filter. After passing through the filter to remove larger organisms, the ballast water flows into the UV chamber to destroy smaller organisms. During de-ballasting, the water bypasses the filter but again flows through the UV chamber where further irradiation kills any remaining microorganisms.

The entire system has a very small footprint and can be mounted at any angle, making it easy to install even in the confined spaces of a vessel’s equipment room. Once installed, the system requires little effort to operate by the crew. It can be controlled by a master PLC unit which can be integrated into the vessel’s machinery automation network. The UV unit is equipped with automatic wipers to keep the UV lamps clean, and the only maintenance required by the crew is the replacement of the UV lamps once a year and occasional preventative maintenance procedures.