APPENDIX F Candidate Shipboard Treatment Technologies: Supplementary Information
The supplementary information on thermal, electric pulse/pulse plasma, and acoustic technologies provided in this appendix is based primarily on data presented to the committee by equipment suppliers, technology developers, and research organizations. The information draws extensively on the responses to the treatment options query (see Appendix G).
High temperatures are commonly used to sterilize water in a wide variety of applications. The use of heat treatment to kill potentially harmful marine organisms in ships' ballast water is currently under investigation. Most research to date has been conducted in Australia, where the focus is on killing toxic dinoflagellates.
In the course of ballast water change trials on the 147,000-metric-ton bulk-ore carrier, Iron Whyalla, it was observed that the saltwater overboard discharge from the main engine coolers was sterile. Subsequent laboratory tests showed that dinoflagellate cysts of Gymnodinium catenatum are destroyed when exposed to temperatures of 45°C for a few minutes. The latest laboratory research indicates that exposure to temperatures of 35°C for approximately 12 hours may be sufficient to kill dinoflagellates. Controlled shipboard experiments were conducted on the Japanese vessel, Ondo Maru, to determine whether the water in ballast tanks may be sterilized over a long sea voyage by continuous flushing with ocean water heated to approximately 35°C. However, the test results were not conclusive.
Thermal treatment has also been investigated in the course of research directed toward finding methods for environmentally sound control of zebra mussels.
Available data suggest that heating water to the acute upper lethal temperature of zebra mussels (typically in the range 38°C to 43°C depending on the acclimation temperature), followed by a rapid return to normal temperatures, is a promising mitigation technique for zebra mussel fouling.
Heat treatment of ballast water is potentially attractive because (1) waste heat from the ship's engine is a possible energy source for heating ballast water, and (2) no chemical byproducts or residuals are discharged. Shipboard implementation of thermal treatment would only require additional pipework and possibly an additional pump, starter, and electrical wiring to allow the hot water to be pumped through the ballast tanks using the flow-through method. As discussed in Chapter 4, a number of critical factors will probably limit the use of thermal treatment to certain vessels on specific trade routes. These factors include voyage time, the volume of ballast water to be treated, the ambient water temperature, and specificity to target organisms.
There would be no special safety requirements since the equipment needed is standard shipboard kit.
Higher organisms such as fish are more easily killed by thermal treatment than microbes. Current work focuses on destroying toxic dinoflagellates, and studies will be needed to determine the effectiveness of heat treatment in killing other specific target organisms. An advantage of the proposed flushing method is that the proportion of original sediment in the ballast tanks is reduced, thereby enhancing the overall effectiveness of the treatment.
Status of Technology
Heat treatment is a well-known technology for land-based applications, but its use on board ship is at a research stage with the aforementioned Ondo Maru trials. Shipboard implementation will require the installation of a suitable marine system and definition of treatment parameters (temperature and time) to establish the success of thermal treatment in sea-going conditions.
The possibility of using various shipboard waste heat sources has been considered for the case of the bulk ore carrier, Iron Whyalla.1 There are a number of
possible options for using the 5.7 MW power potentially available from the main engine cooling circuits. Heating the ballast water on a once-through basis during ballasting or deballasting is not practical from an energy standpoint. Further, the main engine is not normally operating during these ballasting operations. Recirculation of ballast water during a voyage requires much less power, although temperatures would be limited, possibly to less than 40°C. Heating of the water in the ballast tanks by continuous flushing with heated ocean water is potentially the most attractive option for the Iron Whyalla, particularly if the ''lower temperature, longer time" treatment proves effective. Energy consumption would be continuous to maintain the temperature of the ballast water at the required level for the necessary time.
Although thermal treatment does not involve the discharge of chemical byproducts and residuals, the release of heated water from ballast tanks may be of environmental concern (see Chapter 4). In addition, it may be necessary to filter out dead organisms following treatment.
The cost of additional pipework and pumps for a 147,000-metric-ton bulk carrier with about 60,000 metric tons of ballast water has been estimated at $50,000.2
Size, Complexity, and Maintenance
For the case cited above, the small additional pump needed could be readily accommodated on board ship. The complexity of the system would be standard for shipboard use. Maintenance requirements would be minimal.
A simple, shipboard test is needed to support the heat treatment option. It may be possible to monitor temperature versus time as an indicator of treatment effectiveness.
ELECTRIC PULSE AND PULSE PLASMA TECHNIQUES
Pulsed electric field technology is being investigated as a means of preventing biofouling of water intake pipes on ships and at shore-based facilities. Water is passed between two metal electrodes and subjected to an electric pulse on the
order of one microsecond duration with 10 kV applied to the electrodes. Early laboratory tests have been designed to provide reproducible data showing the effect of pulse length, voltage, and water salinity on treatment effectiveness. Experiments to date have used brine shrimp Artemia salina, which can be either stunned or killed depending on the pulse voltage and duration. Other studies have shown submicrosecond electric pulses to be lethal to bacteria (Escherichia coli).
Pulse plasma technology is being evaluated for the treatment of sewage and other waste water. The method is based on existing pulse plasma discharge systems used in a variety of industrial applications, notably metal forming. Adaptation of the technology to water treatment involves delivering a high energy pulse to an in-water arc mechanism and generating a plasma arc in water. The pulse plasma arc discharge produces a short energy burst at very high power density across the electrode gap, generating an arc channel containing a highly ionized and pressurized plasma, which in turn transfers energy to the water via dissociation, excitation, and ionization; and a rapid temperature rise at the arc front. The discharge is an efficient method of promoting pyrolytic, hydroxyl radical, free electron and ultraviolet generated reactions in water. Additional destruction of biological material is likely to result from direct reaction of hydrated electrons due to the release of soft x-rays and high-energy ultraviolet radiation from the energized plasma. The intense cavitation events induced by shock waves may aid in the destruction of living organisms in the proximity of the arc discharge.
The high-voltage portion of an electric pulse treatment system can be encapsulated such that no high fields exist outside the treatment volume. As with any high-voltage device, hazards can be avoided with proper grounding and insulation.
Pulse plasma systems use pulse voltages on the order of 15 to 25 kV. In addition, the plasma produces electromagnetic radiation (ultraviolet and soft x-rays) and a high-pressure shock wave. Shielding, screening, and access panel interlocks would be required to ensure the safety of personnel.
The ability of electric pulse treatment to kill a broad spectrum of species has not yet been demonstrated. For brine shrimp, 95 to 99.9 percent sterilization is claimed. The percentage sterilization may be increased by raising the energy per pulse (and associated power requirements).
Pulse plasma technology is reported to achieve 99.9 percent (or greater) sterilization. Increased treatment times (and power requirements) help assure that all life in the water is destroyed. The treatment is sensitive to the presence of sediment, although the performance degradation due to sediment is claimed to be less than for ultraviolet treatment.
Status of Technology
Electric pulse technology is at an experimental level. Work to date has been limited to laboratory tests and testing of a prototype system in a harbor. Scale-up may be an issue.
Pulse plasma technology for water treatment is at the exploratory development stage. Laboratory devices have been built, and the scientific validity of the method is under investigation. Although the plasma arc device is a mature technology, it is the committee's understanding that it is not used to any significant extent in the marine industry.
The electrical energy needed to kill brine shrimp has been determined experimentally as 1 J/cm3 for a pulse duration of 3 x 10-5 s. It is anticipated that such energy densities would be sufficient to kill any organism found in ballast water, with the exception of bacteria. For System A (see Chapter 4 and Appendix G), an electric pulse system providing approximately 600 kW average power would be needed.
Power consumption for a typical pulse plasma system is in the range 25 to 50 kW. Since the technology is currently only suitable for low flow rates, either multiple systems or recirculation would be required to handle typical ballast water treatment needs. Thus, power consumption could increase significantly.
Theoretically, pulses of electricity in salt water can generate chlorine electrolytically. However, no chlorine has been detected in electric pulse experiments conducted to date.
When in operation, pulse plasma systems vent gaseous decomposition products (primarily carbon dioxide). Sedimentation may be increased, depending on the marine life and compounds present in ballast water, and some filtration process may be needed to prevent degradation of treatment effectiveness. No toxic byproducts or residuals have been detected.
The capital cost of an electric pulse system for treating ballast water is estimated at $350,000, with a treatment cost of approximately $360 for a tank containing 25,000 m3 of water.
Estimated costs for a pulse plasma treatment system are in the range $100,000 to $200,000, exclusive of installation. Operation and maintenance costs are estimated at around $150/hour, including electrode replacement but excluding the cost of electrical power. Ignitron replacement after 10,000 hours of operation would cost about $5,000.
Since both electric pulse and pulse plasma treatment technologies are relatively immature, the above cost estimates are clearly very approximate.
Size, Cost, and Complexity
An electric pulse treatment system that meets System A requirements would be approximately 2.5 m wide, 1.5 m high, and 1.0 m deep, and weigh about 1.5 tons, mainly due to the transformers. Such a system would be designed for long lifetime (more than 105 hours), and no maintenance would be required over this period. Since the system would be a push-button device, no training in its use would be needed.
The gross volume of a pulse plasma treatment unit for System A would be between 4 and 6 m3, with a weight of about 4,500 kg, including safety screening and controls. Such a system would be self-monitoring with automated shutdown and out-of-service alarms, and would not require attended operation. Maintenance could be scheduled while a vessel was in port, but no information is available on the mean time between failures. One or 2 days of training would be needed to acquaint engine room personnel with the device and its safety provisions.
Both systems monitor energy flow, but additional tests (and equipment) would be needed to measure the mortality rates of specific organisms.
Ultrasound in the appropriate frequency and power ranges destroys microorganisms in liquids by means of localized mechanical stresses resulting from cavitation. Ultrasonic treatment systems use transducers to generate alternating compressions and rarefactions in the liquid to be treated. The resulting cavitation is influenced by frequency, power density, time of exposure, and the physical and chemical properties of the liquid. Optimum frequencies for destroying microorganisms are reported to be in the lower range of ultrasonic frequencies, from 15 to 100 kHz. The application of ultrasound treatment to large volumes of liquid has given variable results. Treatment effectiveness decreases with increasing distance from the transducer as the energy density in the liquid decreases. The efficacy of ultrasonic treatment increases with exposure time and can also be influenced by resonance effects due to container geometry.
Any shipboard ultrasonic treatment system would be fully sound-insulated and shielded, even though the operating frequencies are not considered harmful.
An appropriately designed ultrasonic system could totally destroy a broad spectrum of fungi, yeasts, and pathogenic bacteria. As regards higher organisms, pilot-scale ultrasonic treatment tests on zebra mussel veligers in water flowing at rates between 50 and 500 gpm gave variable results. The kill rate was small for short treatment times (less than 60 s), but increased to 100 percent with a treatment time of 12 min. It was concluded that such a system would not be practical for a power-plant intake application. It has been shown that high frequency sound (approximately 125 kHz) consistently elicits strong avoidance responses from certain fish (alewives [Alosa pseudohargenus ] and juvenile American shad [Alosa sapidissima]), but the fish are not killed on entering an ensonified region.
The committee concluded that, despite encouraging results in killing microorganisms, the limited effectiveness of acoustic methods in destroying higher organisms renders this technique generally unsuitable for shipboard ballast water treatment.
Status of Technology
Ultrasound has been used to control micro-organisms in the food, dental hygiene, and water-treatment industries. A feasibility study was conducted in the mid 1970s using ultrasound for shipboard waste water treatment, but effective cavitation and resulting sterilization were not achieved for the volumes of water involved. Given the importance of the treatment chamber and geometry in determining treatment effectiveness, it is clear that a large-scale shipboard system would need to be carefully designed. The possibility of using ultrasound to destroy micro-organisms in shipboard fuel systems is currently under investigation. A prototype system capable of handling 3,000 gal/hr is under development. Current ultrasonic systems could not handle the anticipated ballast water flow rates of 2,000 to 20,000 m3/h in a shipboard environment, and scale-up is likely to be problematic. Acoustic treatment—if deemed appropriate for specific applications—would be more readily implemented at a shore-based treatment facility with adequate tank storage. A closed-down oil refinery or tank farm might provide an appropriate configuration.
McMahon, R.F., M.A. Matthews, T.A. Ussery, R. Chase, and M. Clarke. 1995. Further Studies of Heat Tolerance of Zebra Mussels: Effects of Temperature Acclimation and Chronic Exposure to Lethal Temperatures. Technical Report EL-95-9. Vicksburg, Mississippi: U.S. Army Engineer Waterways Experiment Station.
McMahon, R.F., and T.A. Ussery. 1995. Thermal Tolerance of Zebra Mussels (Dreissena polymorpha) Relative to Rate of Temperature Increase and Acclimation Temperature. Technical Report EL-95-10. Vicksburg, Mississippi: U.S. Army Engineer Waterways Experiment Station.
Rigby, G., and A. Taylor. 1993. Shipping Ballast Water—Heating as a Means of Destroying Potentially Harmful Marine Organisms. Technical Note BHPR/ENV/TN/93/005. Melbourne, Australia: BHP. (See also references therein.)
Taylor, A.1995. Personal communication to the Committee on Ships' Ballast Operations, Washington, D.C., October 3.
Electric Pulse and Pulse Plasma Techniques
CASRM. 1995. Response to treatment options query received from the Center for Advanced Ship Repair and Maintenance, Old Dominion University, Norfolk, Virginia.
EPI. 1995. Response to treatment options query received from Enviro-Plasma, Inc., Fairfax, Virginia.
DREA. 1994. Ultrasonic Destruction of Micro-organisms in Shipboard Fuel Systems. Report DREA CR/94/440. Halifax, Nova Scotia: AASTRA Aerospace, Inc. for the Defence Research Establishment Atlantic, Canada.
DREA. 1995. Response to treatment options query received from Defense Research Establishment Atlantic, Halifax, Nova Scotia, Canada.
ESEERCO. 1993a. Reducing Impingement of Alewives with High Frequency Sound at a Power Plant Intake on Lake Ontario, volume 1. Research Report EP 89-30. Schenectady, New York: New York Power Authority, Sonalysts Inc., BioSonics Inc., and EA Engineering, Science and Technology, for Empire State Electric Energy Research Corporation.
ESEERCO. 1993b. Pilot Scale Acoustic Control of Zebra Mussels. Research Report EP 91-17. Schenectady, New York: Sonalysts Inc. for Empire State Electric Energy Research Corporation.
Kenna, M. 1995. Acoustic Solutions to Environmental Problems. Presentation to the Committee on Ships' Ballast Operations, Washington, D.C., August 22.
Sonalysts, Inc. 1995. FishStartle™ Acoustic Fish Deterrent System. Waterford, CT: Sonalysts, Inc.