How a ballast water treatment system works

Malcolm Latarche
Malcolm Latarche

10 March 2017

When a ship is sailing in empty or part laden condition, its ballast water treatment system allows the propeller to be submerged ensuring more efficient use of the ship’s engine. Even when ships are in a loaded condition, small amounts of ballast can be used to ensure optimum trim improving fuel efficiency by as much as 5% if the conclusions of developers of trim optimisation software are accurate.

Ballast is also used for other operational reasons on occasions and in special circumstances. More about the latest ballast water regulation can be found here. Examples include maintaining optimum distances between loading and discharging apparatus such as conveyor belts, altering the attitude of a ship to carry out repairs to the hull while still afloat and carrying out similar actions to raise breaches of the hull above the waterline after a collision or other cause of damage.

A typical ballast water treatment system consists of tanks located in the double bottom or void spaces in a double hull or as wing tanks in bulk carriers. In some ships, ballast tanks may be located athwartship between cargo holds.

Pumps are used to move the water from the intakes to the chosen ballast tanks although it is possible in many ships to take ballast into the double bottom tanks by gravitating without using the pumps.

The tanks are fitted with a means of releasing air as they are filled usually through pipes with a non return valve to prevent water ingress into the tanks from above.

Depending on ship size and type, the number of pumps may vary, large vessels usually have two. The pumps can generally handle all tanks but commonly one serves the tanks on the starboard side and the other the port side tanks, except in times of need or breakdown.

Filtration of ballast water where no treatment system is fitted can be quite rudimentary and it is not uncommon for ships to collect a large quantity of sediment in the period between drydockings or ballast tank cleaning. Sediment is undesirable as it reduces the earning capacity of the ship and constant movement of larger material can cause damage and wasting of the tanks. It also provides a fertile breeding ground for invasive species.

Fitting a ballast water treatment system

On ships built without a ballast water treatment system, space requirements for components of the ballast system are minimal. By contrast, treatment systems can make quite large demands on the space available in the machinery area.

This may be less of an issue for newbuildings than for existing ships as space can be reserved for a ballast water treatment system even if one is not installed at the building stage. It could be argued that all vessels that may have been affected by the deadlines for newbuildings contained in the convention should have been constructed with this in mind although a small number probably have not.

There have been several proposals for building ships that do not make use of water ballast but the idea has gained little traction. Japanese classification society ClassNK has gone as far as granting AIP (Approval in Principle) to one such system the MIBS (Minimal Ballast Water Ship) VLCC design developed by Namura Shipbuilding in cooperation with the Shipbuilding Research Centre of Japan.

Namura’s MIBS VLCC design, addresses the challenges via the use of a revolutionary new hull form, which greatly reduces the amount of ballast water necessary for safe operations. The design reduces the weight of ballast water required in normal ballast conditions by around 65%, paving the way for the use of smaller ballast water treatment systems and reducing fuel consumption.

The MIBS design builds on a previous Non-Ballast Water Ship (NOBS) design project promoted by the Japan Ship Technology Research Association as part of a Japanese national project. While the NOBS project succeeded in creating tanker designs which could operate without the need for ballast water, the extremely wide hull shape limited its commercial applications.

The MIBS design however, incorporates features from the NOBS design with a flatter bottom and standard breadth hull. This allows for a dramatic reduction in the amount of ballast water needed, while maintaining the dimensions of a standard VLCC. Although the designs are theoretically sound, they have not been commercially accepted and no vessels have yet been built.

Another proposal would see the return of solid ballast particularly in container ships with the ballast being in containers that would be placed at the bottom of stacks under cargo containers. Such concepts have generally been disregarded by ship operators as impractical and not addressing the issue of ballast being also used for trim adjustments for operational and safety reasons.

Ballast water treatment system ashore

Since the issue of ballast first became a hot topic, some innovative thinking on the issue has been applied. As well as the no ballast on board or minimal ballast option, there have been a number of proposals advocating all ballast should be supplied from and treated ashore.

While this would be a solution in many ports, it would seem that the operational use of ballast may not have been fully taken into account. There are many ports where ballast needs to be discharged and re-taken in order to negotiate obstacles such as bars and shallow approaches. Also in ports where a river or canal passage in fresh or brackish water is unavoidable, the ballast may need to be altered to aid buoyancy.

Shore-based ballast treatment does however show promise in a variety of operational scenarios. It could be used in an emergency when a ship’s own ballast treatment system is faulty or damaged or for ships on fixed routes or those calling at ports where there is a straightforward navigational approach it could even negate the need for ballast treatment on board if facilities exist at all ports served.

As mentioned above, a recent US Court decision specifically mentioned that the use of port reception facilities should have been considered by EPA when that agency formulated the 2013 VGP. A future change of thinking may see US ports equipped with reception facilities but that is not something that can be relied upon by operators at the present time.

There are numerous shore-based solutions that are being seriously proposed and considered. The first, and possibly the oldest, is the HTM Aqua-Therm system proposed by Australia-based Hi Tech Marine. Like its onboard system SeaSafe-3, the Aqua-Therm concept involves the use of waste heat to disinfect ballast discharged from ships or supplied to ships.

The company suggests that where a local source of waste heat such as a factory, power plant or similar exists, a joint project with the port concerned could have advantages for all parties especially in regard to cost saving.

Another option proposed by India and first discussed at MEPC 66 in March 2014 is for a ballast water treatment barge that would take ballast from ships, treat it using an onboard system and then discharge to a shore facility.

There was some disagreement as to whether the barge should itself be fitted with a treatment system but the opinion of the Ballast Water Review Group established during the session was that discharge to a Ballast Water Boat is not an alternative method but equates with discharge to a reception facility. Guidelines for reception facilities are already in place (IMO G5).

The third is a containerised treatment unit first developed by Dutch shipbuilder Damen but since adopted by others. The company’s proprietary InvaSave Technology allows treatment at the point of ballast water discharge in contrast to fixed onboard installations that also need to treat ballast water at intake. It is based on continuous fine filtration combined with Ultra Violet treatment.

Sludge and sediment is dewatered and compacted in a secondary treatment so it can be safely further processed ashore. Damen can deliver the system as a self-sufficient mobile container, which can be put on board of a Damen Ballast Water Treatment Vessel or be moved around the port on a trailer, a pontoon or other types of vessels. Each (lDamen InvaSave 300 container unit handles 300 m3/h with scaling up if required achieved by using multiple container units. Land-based test have been completed and the containerised version is currently undergoing tests on board a small container ship. Damen uses systems from other manufacturers including from French manufacturer Bio-UV.

Another Netherlands-based company UniBallast offers an installation service for all ballast water treatment system and can also arrange for a system of the customer’s choice to be containerised. The ballast water treatment system has been designed to be shipped with a vessel or even by air freight, because the skid is lightweight and it is used for small vessels with a ballast water capacity of around 100m3. The unit has a low power usage so can be directly connected to the ship’s system using an electrical plug. UniBallast says it can customise any ballast water maker’s application as long as they have sufficiently small components to fit in the skid.

Larger systems can be housed in 20’ or 40’ boxes. UniBallast has developed a Universal Ballast water Port Connector which has been type-approved and comes in many sizes (4” - 12”). The ballast water treatment skid will be connected via a flexible rubber hose to the UBPC which has a tie-in to the existing hard piping of the ship’s ballast water system. The ballast water pump is used to pump ballast water through the treatment unit to get cleaned and pumped overboard.

A containerised treatment ballast water treatment system that could be used on board ships either as the only system or in place of a faulty system would solve many of the problems associated with the issue of ballast treatment.

It could, for example, allow a vessel that has been granted an exemption as an end of life ship to enjoy an extended life span or it could be used for a vessel that is exempted as normally trading in a confined area to trade outside of that area on a temporary basis.

Container mounted systems could also be switched between vessels as a cost saving measure but more importantly they make sense because a system can easily be removed from an end of life vessel and reused rather than ending as scrap metal. They could also have a second application as means of providing clean treated water in third world countries.