The introduction of aquatic nuisance species into coastal marine and estuarine waters occurs due to a variety of sources. However, because of the high volume of maritime traffic and the large quantities of water involved, ballast water is the most frequently cited cause of the worldwide transference of non-indigenous species (NIS). NIS is defined as any species or other viable biological material that enters an ecosystem beyond its historic range, including any such organism transferred from one country into another.
Ballast water exchange is presently the only regulated method to control NIS transference and it is not completely effective. It is time consuming and a costly method of preventing the NIS transference, while often a dangerous operation depending on conditions. With international, national, state and local environmental agencies worldwide taking action to regulate the discharge of ballast water arriving in ships coming from overseas ports, a variety of ballast water treatment technologies are proving effective at treating ballast water with no adverse effects on the environment.
Technologies used for treating ballast water are typically identified as solid-liquid separation, disinfection or some combined form of both treatment schemes. Solid-liquid separation uses sedimentation or surface filtration to separate suspended solid material (inorganic and organics including some larger targeted NIS zooplankton and phytoplankton) from the ballast water. Disinfection inactivates and/or kills the remaining microorganisms from ballast water using some form of chemical or non-chemical process. A number of commercially available ballast water treatment technologies have been modeled after comparable treatment systems often used in municipal and industrial water and wastewater treatment applications. However, these technologies have been adapted to meet marine-specific criteria such as space, weight, cost and efficacy with respect to discharged ballast water standards.
Ballast water regulations help ensure treatment systems are developed and marketed to meet the same discharge standards. And, testing and certification of ballast water treatment systems to such standards aids in standardization of approved, commercially viable technology. So, when individual ballast water treatment systems are equally able to meet the same discharge limits, key technical and commercial features of a particular technology become the distinguishing factors in selection. Examples of key criteria affecting capital and operating expenditures include flow capacity, footprint, weight and power consumption.
A large percentage of ballast water treatment technologies have been developed for flow rates starting at approximately 250 m³/hr – the flow considered most common for vessels requiring compliance under the first phase of ballast water legislation. Since most ballast water treatment systems are largely modular in design, they can be scaled up to meet larger flow rates of 5,000 m³/hr or more. However, because many of these systems are multiple duplications of smaller units, size and cost can vary greatly when accommodating higher flow rates.
BALPURE®: cost-efficient biocidal treatment of ballast water
In 1996, the National Research Council identified the use of biocides as an option for treatment of ballast water. One biocidal ballast water treatment system that excels at treating high-flow-rate applications with an economically viable, lightweight and space-saving design is the BALPURE system from Severn Trent De Nora. The patented BALPURE system generates biocides, meters and analyzes the residual level of both biocides and neutralizing agents, logging the performance of the overall ballast water treatment system for compliance and reporting requirements. As a result, the use of hazardous chemicals is not required with the BALPURE system. Systems accommodate flow rates 250 – 5,800 m³/hr in varying configurations (packaged, containerized and modular), and larger units can be provided to meet application-specific needs. Modifications are minimal to the existing ballast water system making the BALPURE system ideal for retrofit additions of ballast water management systems.
BALPURE is used during ballasting to filter and disinfect incoming seawater and during de-ballasting to neutralize residual oxidant in discharged seawater. During ballasting, a side stream of main flow is used to generate oxidants, the main flow is filtered to return silt/sediments and large organisms back to the uptake location, oxidants are injected back into the main line and an analyzer/data logger is used to monitor/control residual oxidant. A TOC analyzer is used to monitor and predict uptake ballast water oxidant demand levels and accurately produce the required biocide for each location. During de-ballasting, sulfite is injected into the main de-ballast line to neutralize residual oxidants with an analyzer/data logger used to control and verify effective neutralization. The system requires approximately four hours of maintenance per month and operates for less than USD $0.02 per m³ of ballast water treated (USD $0.15/kWh generation cost).
The BALPURE system also maintains a residual oxidant until final de-ballast. Competitive technologies unable to offer a residual (such as ultraviolet disinfection) will likely have to treat during ballasting (uptake) and de-ballasting (discharge). Without a measurable residual, these technologies also have no simple way to confirm efficacy. These are important considerations, especially when determining operating costs to install a ballast water treatment technology and confirming to any state port authority that ballast water management is being properly conducted.
The BALPURE system is designed to continuously meet the oxidant demand of the ballast water during uptake, ensuring a reliable residual value to alleviate re-growth of algae/fungus in the ballast water storage tanks during the duration of a vessel’s journey. The properly instrumented design maximizes the system’s safety margin to ensure complete organism disinfection. Without a residual disinfectant, the interior of the ballast water tank is likely to experience a build-up of algae/fungus growth that will require periodic cleaning and require disinfection upon discharge.
Modularly based competitive ballast water treatment systems will simply replicate their base model design in order to treat increased flow rates, leading to an inefficient use of space and increased costs and system complexity. The BALPURE system uses electrolytic technology to generate the biocide on demand. As a result, increased flow rates can be accommodated by expanding the base model and using larger electrolytic cells to generate greater quantities of the disinfectant required to treat the higher flow rates. The operating and capital cost implications of replication of smaller units are eliminated when the system is fully integrated to the ship’s specific needs.
For example, a 250 m³/hr ballast water system requiring 40 kW of power that is replicated three times to treat 750 m³/hr will then require 120 kW of power. In this example, to treat a total of 7,500 m³ of ballast at 750 m³/h would require 10 hours of operation, thus 1,200 kWh to complete the entire uptake cycle (assumes 100 percent of ballast water is loaded). This high energy consumption is made worse if that system does not offer some form of residual disinfection, making treatment for both uptake and discharge cycles a requirement. That would then require a total of 2,400 kWh.
Compare this to the BALPURE ballast water treatment system which offers residual disinfection and is capable of being expanded to treat between 250 and 750 m³/hr, requiring 41 kW of power (maximum for the 750 m³/h, less for the 250 m³/h flow rates). Following the earlier example, to treat the 7,500 m³ of ballast water would only require 410 kWh -- approximately 83 percent energy savings. Additional energy savings can be realized by reducing biocide generation by closely monitoring the uptake TOC and operating the BALPURE with less power so that only the required biocide is generated to meet the demand.
The BALPURE 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 has confirmed effluent quality that meets proposed International Maritime Organization ballast water standards.
There are three certifications required to develop a commercially salable ballast water treatment system: Basic, Final and Type Approval. The BALPURE system's completed Basic dossier was submitted to the International Maritime Organization (IMO) via BSH/Germany in August 2009 – in time for the MEPC 60 conference (March 22–26, 2010). The BALPURE system is expected to have Basic Approval by March 2010 (MEPC 60) and Final Approval by October 2010 (MEPC 61). Severn Trent De Nora is working with ship owners to complete shipboard mechanical and efficacy tests to obtain Type Approval, projected to be completed early in 2011.
For more information, e-mail info@severntrentservices.com.
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