A considerable threat to America’s marine environment is the introduction and spread of aquatic nonindigenous nuisance species. Defined as a species that has been introduced into an area beyond its native range, exotic vegetation and animals can cause losses of native species, changes in community structure and function, and alterations of the physical structure of the system. Unlike chemical pollution, once a nonindigenous species establishes itself it is nearly impossible to remove, and can even increase in abundance and spread to new locations.
Invasive species have become established in waters throughout the United States. For example, zebra mussels are present in the Great Lakes and inland waters including the Mississippi River, Hudson River and Lake Champlain. Other exotic species infestations, such as the brown mussel, mitten crab and Eurasian watermilfoil, also have been found in the country’s rivers and lakes.
A major cause of the introduction and spread of these nonindigenous species is ships' ballast water – the water carried by ships to provide stability and adjust a vessel's trim for optimal steering and propulsion. Ballast water is often taken in by a ship in ports and coastal regions, where the ecosystems include many forms of bacteria, plankton, plants and animals. Ballast water then is released during various stages of the ship’s journey such as at sea, along coastlines and in ports. As a result, a wide variety of nonnative species is transported and distributed around the world.
Agencies such as the International Maritime Organization (IMO), United States Coast Guard (USCG) and state governments are currently fighting the problem by examining ballast water exchange in the open ocean or utilizing ballast water treatment systems. Thus far, only the IMO has mandated such an exchange of ballast water. The USCG is using two programs to evaluate treatment technologies: the Shipboard Technology Evaluation Program and the Environmental Protection Agency’s (EPA) Environmental Technology Verification (ETV) program.
One of the first systems evaluated by the ETV program has been Severn Trent De Nora’s BALPURE® ballast water treatment system. The system, which received a U.S. patent last October, generates biocides, identified in 1996 by the National Research Council as an effective option for treatment of ballast water. The BALPURE system meters and analyzes the residual level of both biocides and neutralizing agents and logs the performance of the overall ballast water treatment system. The system has proven to be an effective, economical and high-capacity device to treat ballast water with no adverse effects on the environment. Third party testing of the BALPURE system -- including a full range of EPA-specified whole effluent toxicity tests and disinfection by-product analyses – has confirmed effluent quality that meets proposed IMO ballast water standards.
The BALPURE system is utilized during both ballasting (to disinfect incoming seawater) and de-ballasting operations (to neutralize residual oxidant in discharged seawater). In the ballasting process, a small side stream of the main ballast line is delivered to the BALPURE system where there is a slight increase in line pressure. The seawater passes through a flow orifice and flow transmitter that provides confirmation of proper seawater flow to the unit. The seawater passes through the system’s electrolyzer utilizing proprietary electrode coatings, generating oxidants (hypochlorite and hypobromite derivatives). The solution of depleted seawater, oxidants and hydrogen gas then passes through a patented cyclone and the hydrogen is safely separated and diluted. The oxidants are injected back into the main ballast stream on the discharge side of the ballast pump(s), matching the seawater oxidant demand. The biocides react in the pipe with both inorganic and organic species in the ballast water to provide effective disinfection. As the harmful organisms and nonindigenous species are inactivated and/or destroyed, the oxidant concentration in the ballast water is reduced to one part per million (ppm). Testing has proven that this initial concentration of oxidants will guarantee a greater than 99% destruction and inactivation of organisms and bacteria in the ballast tanks.
During the de-ballasting process, sodium sulfite is added in a controlled fashion to the suction side of the de-ballast pump, which instantly reacts and neutralizes residual oxidants. The treated ballast water may be safely discharged into the receiving ecosystem, and the sulfite can be added to the discharge of the de-ballast pumps if they are contained within the ballast tanks. Independent laboratory studies have proven that the low concentration of sodium sulfite used in the BALPURE process is not harmful to fish, fauna, bacteria or the ecosystem as a whole.
The generation of biocide, the injection operation, and the neutralization step are all recorded in a data logger and can easily be downloaded by port authorities to confirm that a successful ballast water treatment has been conducted and residual biocides have been destroyed prior to discharge of the ballast water.
In addition to the BALPURE system, a number of other methods are being analyzed for possible inclusion in an anticipated ballast water standard. These include other chemical treatment methods; mechanical methods such as filtration and separation; physical treatment methods such as ozone and ultraviolet light; and various combinations of these methods. According to some maritime industry officials, publication of a new standard may occur before the end of this year.
For more information, e-mail info@severntrentservices.com.
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