What is ballast water?
Ballast water is used to stabilise vessels and maintain their structural integrity. Typically ballast water is pumped in to special tanks while cargo is being unloaded, and discharged while cargo is being taken on board. Safety, weather conditions, the ship’s load, and the route taken are the primary factors that determine how much ballast water is taken on board a vessel for a particular voyage. More ballast is necessary for ships to sit lower in the water during stormy weather to avoid bottom impact from waves. Ballast water is also adjusted so as to balance the ship as it consumes fuel during a long voyage.
What is ballast water treatment?
Ballast water treatment is the process of treating ballast water in order to actively remove, kill and /or inactivate organisms prior to discharge. Ballast water treatment is different from the older process of ballast water exchange, which involved completely flushing the ballast water tanks during voyages in open water with sufficient water depth and distance from shore.
What is ballast water treatment needed?
Ballast water taken on in one ecological zone and released into another can introduce invasive and nuisance aquatic species that may have detrimental impacts on the biodiversity, economy or human health of the receiving community and may in time become a serious threat to the environment.
Bio-invasion is one of the four greatest threats to the world’s oceans today, alongside land-based sources of marine pollution, the over exploitation of living marine resources and the physical alteration and destruction of marine habitats.
More than 90 per cent of global trade is carried by sea, and each year transfers of up to 12 billion tonnes of ballast water take place around the world. In order to reduce the incidence of bio-invasions, ballast water treatment reduces or renders inactive 99.9% of the living organisms in the ballast water.
What is included in the type approval process?
Technologies developed for ballast water treatment are subject to approval through specific processes and testing guidelines designed to ensure that such technologies meet the relevant standards. The approval consists of both land-based testing of a production model to prove that the discharge standards are met, and shipboard testing to prove that the system works in service.
The most relevant guidelines are the IMO G8 Guidelines “GUIDELINES FOR APPROVAL OF BALLAST WATER MANAGEMENT SYSTEMS (G8)” and G9 “PROCEDURE FOR APPROVAL OF BALLAST WATER MANAGEMENT SYSTEMS THAT MAKE USE OF ACTIVE SUBSTANCES”. These technical guidelines are issued by the International Maritime Organization (IMO) and outline an evaluation procedure (including land- and ship-based testing) that equipment must undergo to demonstrate that it meets the ballast water discharge standards set out in the Ballast Water Management Convention.
In addition, systems that apply for US Coast Guard Type Approval must be tested according to the “ETV Generic Protocol for the Verification of Ballast Water Treatment Technology”. The ETV protocol is similar to the G8 guidelines in that it contains evaluation procedures for system testing. However, it is much more prescriptive.
How can the transport of small organisms evolve into such huge problems?
There are thousands of marine species that can be carried in ships’ ballast water; basically anything that is small enough to pass through a ship’s ballast water intake ports and pumps.
The problem is compounded by the fact that virtually all marine species have life cycles that include a planktonic stage or stages.
Even species in which the adults are unlikely to be taken on in ballast water, for example because they are too large or live attached to the seabed, may be transferred in ballast water during their planktonic phase.
The biodiversity, large numbers and prevalence of a planktonic phase for most species, are the primary factors that significantly increase the risk of bio-invasion via ballast water transfer.
The difference between ballast water exchange and ballast water treatment
This FAQ is aimed at the crew onboard a ship that has ballast water tanks and only addresses, in a birds view, the operational differences and the main technical differences. The biggest difference is that Ballast Water Exchange is done in mid ocean, where Ballast Water Treatment is done in port during the cargo handling operations.
Ballast Water Exchange
Ballast Water Exchange is a very demanding procedure which required a tedious preparation because each exchange method has its own pros and cons. All procedures require continuous attention to keep the vessel and her crew safe. Points of attention are keeping the propellers submerged, keeping the hull stress within limits, maintaining the visibility for safe navigation, maintaining the (intact) stability, preventing possible slamming of the bow, etc.
Most of the crew sailing on ships with ballast water tanks already use a Ballast Water Exchange (BWE) method to comply with regulations. A quick recap learns us that Ballast Water Exchange is a method where coastal or port water is replaced by mid-ocean water during the voyage. Ballast Water Exchange methods in use are known as:
Sequential exchange, where the ballast water tanks are made empty and filled with mid ocean water;
Flow through exchange, where the mid ocean water, in three complete cycles, is pumped through in the tanks while the coastal ballast water leaves the tank simultaneously through the overflow;
Dilution method, where the mid ocean water, in three complete cycles, is pumped in through the top of the ballast water tank, and where the coastal ballast water leaves the tank simultaneously through the bottom connection of the tank.
The whole process and requirements are laid down in a Ballast Water Treatment Plan where the execution of the Ballast Water Exchange procedures are recorded in a Ballast Water Record Book which is to be kept up-to-date and available for review and survey by the port authorities or there representative.
Ballast Water Treatment
Ballast Water Treatment is often, when started up, a fully automatic procedure which have to be monitored for correct operation. When Ballast Water Treatment is applied, there is no more need to apply the Ballast Water Exchange procedures. Of course Ballast Water Exchange can be used, after approval for contingency operation. Many vessels are in the process of or have already been retrofitted with a ballast water treatment system. A typical retrofit installs a ballast water treatment in the existing ballast water system.
Depending on the system in use, ballast water treatment is required at ballast water uptake and during ballast water discharge. Damen Green has partnered with three suppliers, two are specialized in continuous filtration and UV disinfection and one has specialized in continuous filtration with electro-chlorination. The electro-chlorination system is derived from the well-known Chloropac system for seawater cooling water treatment.
When continuous filtration and UV disinfection, in an automatic and monitored process, is applied; during ballast water uptake, the ballast water is pumped by the own ballast pump through the continuous filter stage followed by UV-disinfection into the selected ballast water tank(s) as usual. During the uptake the filter is automatically cleaned (backwash) while the uptake procedure keeps ongoing. The backwash is pumped overboard by the backwash pump which is part of the ballast water treatment installation. During ballast water discharge, in an automatic and monitored process, the ballast water from the ballast water tanks are pumped with the own ballast water pump through the UV disinfection stage only, overboard as usual.
When continuous filtration with electro-chlorination, in an automatic and monitored process, is applied; during ballast water uptake, the ballast water is pumped by the own ballast pump through the continuous filter stage (main stream) disinfection into the selected ballast tank(s) as usual. Directly after the ballast pump a water sample is taken to determine the amount of Sodium Hypochlorite which needs to be added to achieve the required level of disinfection. The Sodium Hypochlorite is injected in the main stream before the ballast water enters the selected ballast water tank(s). The Sodium Hypochlorite is, in a side stream, made onboard from seawater with the use of an electrolyzer and a degassing module to dilute and release the electrolyzer exhaust gases which are a residue of the Sodium Hypochlorite production. During ballast water discharge an analyzer connected to the ballast water piping before the overboard sea chest, determines the amount of Sodium Hypochlorite left in the ballast water to discharge. If necessary, residual chlorine is automatically neutralized with Sodium Sulphite before it is discharged overboard as usual, if no chlorine is measured, the ballast water is pumped, without further treatment, overboard as usual.
Would it be permitted to treat ballast water only at discharge with a conventional ballast water treatment system, and, for example, to use it in a port as an IMO certified contingency solution?
Unfortunately not, for a number of different reasons:
The type approval certificate of a ballast water treatment (BWT) system describes how it can be used. Normally, for a conventional BWT system, the IMO type approval certificate specifies whether the ballast water is treated before it enters or after it leaves the ballast tank. In case a BWT system is used to treat only at discharge it should be written in the IMO type approval certificate that this is also tested.
The InvaSave is certified and tested specifically for use at the point of discharge. This will also be written in the IMO type approval certificate.
A conventional on board (UV based) BWT system uses a filter during ballast water uptake. Filtration is the critical first step in organism removal. It clears larger organisms while simultaneously removing sediments in the water. The automatic backwash cleans this filter and is discharged overboard. This is permitted since the backwash discharge contains the same organisms as the surface water. In the case that this filter is used (only) at discharge, the backwash will contains different organisms since it is taken in from a different area. Therefore, it cannot be discharged to the surface water.
In the InvaSave container a secondary filtration train is installed, to clean the filter backwash from organisms. Therefore it is permitted to discharge the filter backwash to the surface water with the InvaSave in the case that the ballast water is not from the same area.
A conventional on board (UV based) BWT system is certified according to a standard IMO protocol. This protocol includes the requirement that the ballast water is stored for 5 days (land based tests) in the ballast tanks to allow time for the organisms to respond to the UV treatment. After 5 days the ballast water from the tanks is sampled and the number of organisms are counted. If the numbers are within the limits of the IMO Ballast Water management Convention, a BWT system receives its IMO approval. In the situation that a conventional on board (UV based) BWT system is used only at discharge there is no delay effect for to allow the organisms to die in the tank and the discharged ballast water will probably not meet the IMO standard.
The InvaSave will be IMO certified without the need for storage time of ballast water in the ballast tanks for the die-off of the organisms.