Treatment of Invasive Aquatic Species Found in Ballast Water

By Abbigail Rigdon,
Marine conservation student

As the world becomes more globalized, countries that at one time seemed distant are now easily traveled and easily contacted. Such contact does not exist only between humans, but between other species as well. Sometimes, however, these species can be detrimental to their new environment. Foreign species may be introduced to new environments accidentally (by releasing an exotic pet into the wild, for example), or purposefully (in order to manage an overabundance of a native species by increasing its competition, or by increasing the amount of predators for the species). One major method of accidental introduction is through the release of ballast water from ships.

A docked ship takes on water directly from its environment to ensure stability at sea. The inherent danger of this resides in the fact that the water brings with it plants, animals, viruses and bacteria native to the specific area from where it is acquired. Ballasts are used to hold water from the surrounding area in order to stabilize a ship carrying little to no cargo. When cargo is loaded the boat discharges the water obtained from the previous location, and all of the organisms that “hitched a ride” in the ballast are consequently released into a new location. Most of these species do not survive the trip, and if they do, the action of discharging kills them. In certain circumstances, however, those that do manage to survive may form viable populations that can seriously damage an ecosystem (Tsolaki and Diamadopoulos 2010). While the odds seem unfavorable for these invasive species to survive, they are given plenty of opportunity, as 80 percent of our goods are transported by boat, and approximately 3 to 5 billion tons of ballast water is transferred annually (Tsolaki and Diamadopoulos 2010).

So, what’s the big deal about invasive species? For example, in a few instances, some Floridians intentionally released their pet boa constrictors and pythons (both non-native species) into the wild when they became too large to handle. Subsequently, and quite problematically, the snakes became the top predators in the area because they outcompeted the local predators for food sources (Braun 2009). Fresh and salt waters face similar situations in regards to invasive species. In fact, not only do invasive aquatic species have ecological effects, but they also have economical and human health impacts. With these invasive species out-competing native ones for resources, the native populations are reduced. Fisheries often depend on harvesting these native species to make a profit, and consequently lose money as a byproduct of the invasion. According to Tsolaki and Diamadopoulos (2010), the estimated cost of the impact of all invasive species is more than $138 billion per year in the U.S. alone. Additionally, newly introduced species can be potentially toxic to the area, which, in turn, causes native aquatic species to become ill, and when ingested can cause humans to be sick (Tsolaki Diamadopoulos 2010).
Clearly, invasive aquatic species are problematic, and because so many are transported by ballast water, it makes sense to treat this water in a way that reduces or eliminates these potentially insidious organisms. Tsolaki and Diamadopoulos (2010) view ballast water discharge as a global environmental risk. To address this issue, they reviewed the current methods used for ballast water management that are described below.

Options for ballast water treatment in ships.  Photo: National Research Council (1996). Stemming the Tide: Controlling Introductions of Non-indigenous Species by Ballast Water. National Academy Press, Washington, DC.

Options for ballast water treatment in ships.
Photo: National Research Council (1996). Stemming the Tide: Controlling Introductions of Non-indigenous Species by Ballast Water. National Academy Press, Washington, DC.

Ballast water management can be broken down into two categories: port-based and shipboard (Figure 2).

  1. Port-based treatment involves transferring ballast water to an onshore treatment facility to rid the seawater of non-indigenous species. A visiting ship may then exchange its untreated ballast water for that of the treated seawater. The primary drawback to this method is the fact that ballast water treatment facilities must be constructed first, which is a costly roadblock. Additionally, these facilities necessitate a construction design that encompasses the myriad of treatments used to eliminate marine organisms (physical, mechanical, chemical or a combination). If a port is considerably large and harbors international ships, providing the various treatments specific to every location may become complicated and costly (Tsolaki and Diamadopoulos 2010).
  1. Shipboard treatment involves the use of ballast water exchange or treatment of the ballast water onboard.
  • Ballast water exchange is largely comprised of two methods:

–          Ballast water exchange is a method where ships completely empty their ballast either at one time or sequentially while at sea, and then re-ballast with the surrounding seawater. The idea is that organisms obtained from the open ocean cannot survive the fluctuating conditions of shallow coastal waters.

–          Flow through exchange is a similar method, because old ballast water is exchanged for new seawater. Unlike ballast water exchange, however, this method needs a separate uptake and outflow system to pump mid-ocean water into the ballast, as it permits old water to overflow back to the ocean.

–          While these two methods can be quite effective, not all of these non-indigenous species are eliminated. Some ships have designs that create odd corners and crevices in the ballast that trap organisms. Installing pumps in these areas or designing ship ballasts without these structures would help reduce this problem (Tsolaki and Diamadopoulos 2010).

  • Onboard treatments can be classified as primary and secondary separation techniques.

–          Primary separation employs the use of physical separation such as filtration and cyclonic separation. Ships use a filtration system when ballasting to physically separate organisms from the seawater. Cyclonic separation typically uses hydroclones to sort out aquatic organisms. Hydroclones create a vortex, which causes organisms to be pushed out one way and the clean water another. Hydroclones do not require as much pumping pressure as filtration (Tsolaki and Diamadopoulos 2010).

–          Secondary separation, conversely, uses mechanical and chemical separation to eliminate invasive aquatic species. Some methods of mechanical separation include ultraviolet radiation and heat treatment. UV radiation is used to eliminate viruses and bacteria that can be found in ballast water. Its effectiveness depends on the size and structure of the organism. Thermal treatment involves raising the ballast water temperature to eliminate organisms. This is accomplished by using heat from the ship’s engine or from a backup boiler system onboard. Thermal treatment is considered to be more effective with the intake of ballast water from warmer environments. Microwaves can be used to heat up ballast water as well, and may be more successful than thermal treatment because microwaves have higher heating rates (Tsolaki and Diamadopoulos 2010).

Chemical separation involves the use of biocides, which are chemicals that essentially deactivates an organism by upsetting its biological properties. There are oxidizing biocides, which are used for freshwater systems (chlorine, chlorine dioxide, ozone), and non-oxidizing biocides (formaldehyde, sulfur compounds, glutaraldehyde). The risk with using certain chemical compounds is that they can be hazardous to the environment and should be properly handled (Tsolaki and Diamadopoulos 2010).

No one treatment is 100 percent effective, so Tsolaki and Diamadopoulos (2010) suggest that a combination of any the treatments mentioned would be best. Various methods should be selected depending on the length of the voyage, the operational costs of the different methods, and the impact each method might have on the marine environment (Tsolaki and Diamadopoulos 2010).


Given the foregoing problems and solutions, the United States has taken action in reducing the amount of ballast-carried invasive species by requiring all non-recreational vessels (U.S. and foreign) operating in national waters and equipped with ballast tanks to employ one of five ballast water management methods. These methods include:

1. Installing and operating a ballast water management system that has been approved by the Coast Guard,

2. Using only water from a U.S. public water system as ballast water,

3. Executing a complete ballast water exchange 200 nautical miles away from any shore before discharging the water,

4. Never discharging ballast water in U.S. waters, or

5. Discharging ballast water to an onshore facility or to another vessel for treatment (CFR 151.2025, 2012).


Braun, David (2009). National Geographic. Nine Giant Invasive Snake Species Threaten U.S. Ecosystems, Study Finds. Accessed 30 Oct.

“Navigation and Navigable Waters.” 33 CFR 151.2025. 2012.

Tsolaki E and Diamadopoulos E (2010) Technologies from Ballast Water Treatment: A Review. J Chem Technol Biotechnol 85:19-32 Hyperlink:


1 reply
  1. John Shroyer
    John Shroyer says:

    I am very interested in your field of study. I am a student in the AP Cambridge Capstone Program and I am required to write a research paper. My topic of choice was invasive species and their effect on the environment. I would be honored to have you mentor me with my paper via email. Please respond so that I can continue to write my paper.


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