Ultrasonic Ballast Water Disinfection

The ultrasonic treatment system has demonstrated to be effective in the killing of bacteria, plankton, and larger organisms.
The ultrasonic disinfection of ballast water is a mechanical/ physical treatment, which avoids the dosing of any strong and expensive active chemicals into the ballast water. This ensures an ideal environmental acceptability combined with high biological effectiveness regarding the destruction and inactivation of plant and animal organisms and microorganisms in ballast water.

Background

“If a vessel sails without cargo or partially loaded down, it will need ballast to keep its stability and safety. Water is often used as ballast, but, when it is collected in origin, a series of organisms can travel into the water, normally members of the plankton community which could be stranger in the destination (allochthonous), and they might cause unwanted biogological pollution. In order to avoid this possible pollution, we have to use a effective system to sterilize the ballast water.” [Mingorance Rodríguez: 2012, 163]
Invasive aquatic species are one of the four greatest threats to the world’s oceans, and can cause extremely severe environmental, economic and public health impacts. To avoid the introduction of pest mollusks (zebra mussels, the Asian clam, and others), various treatments of ballast water sterilization (also referred to as disinfection or neutralization) can be applied. A common treatment is the chemical cleaning of ballast water. The chemicals used are environmentally harmful and expensive. With increasing legal regulations for ballast water management, alternative ballast water treatments – e.g. by ultrasonic disinfection – are integrated on board of marine vessels.

Ultrasonic Sterilization of Ballast Water

The ultrasonic ballast water treatment is a mechanical/ physical method, which avoids the use of harmful and expensive chemicals. The cavitational forces kill small aquatic organisms and microorganisms. Several studies have already proven that ultrasound achieves a high level of biological effectiveness on Zebra mussel veliger, nematodes, bacteria, and viruses.

Ultrasonic Cluster with 120kW process power

Ultrasonic Disinfection by Cavitation

High power ultrasound waves generate cavitation bubbles in liquids, which result in intense shear forces and high stress. When intense ultrasound waves are coupled into liquids, the sound waves that propagate into the liquid media result in alternating high-pressure and low-pressure cycles, with rates depending on the frequency. During the low-pressure cycle (phase of rarefaction), high-intensity ultrasonic waves create small vacuum bubbles or voids in the liquid. When the bubbles attain a volume at which they can no longer absorb energy, they collapse violently during a high-pressure cycle (phase of compression). This phenomenon is termed cavitation. During the implosion very high temperatures (approx. 5,000K) and pressures (approx. 2,000atm) are reached locally. The implosion of the cavitation bubble also results in liquid jets of up to 280m/s velocity.
This highly energetic bubble generation and collapse results in hydrodynamic shear forces and ultrasonic oscillations, which breaks and disrupts the cell walls of organisms – effectively killing them.
Concerning its environmental acceptability, there are no known or anticipated environmental concerns associated with the ultrasound-assisted technology.

Biological Effectiveness of Ultrasound

Several studies have proven that ultrasound can affect viruses and bacteria effectively. Disinfection studies with ultrasonic devices to sterilize volume streams of 100 gpm (gallons per minute), equivalent to 23 m3/h, have shown around a 7 log reduction for the Polio Virus (< 5μm) and a 6-7 log reduction for the bacteria Cryptosporidium parvum. With Nematode Heliminth ova, Ascaris (8-10μm) and mollusk zebra mussel veligers (70μm), 100% mortality was achieved. The same mortality rate with zebra mussel has been demonstrated in 600 gpm flow systems (Buchholz et al., 1998).
Inactivation rates of 100% have been achieved in larger organisms and a 6-7 log reduction in bacteria and viruses. With 20 sec exposure in an experimental continuous flow system, 93-98.6% inactivation of Cryptosporidium ocyst and a 4 log reduction at 10 sec. exposure in a laboratory batch reactor has been achieved. Inactivation rates have also been reported for Cryptosporidium parvum (7 log), viable helminth eggs (4.2 log), polio virus (8 log), Salmonella sp. (9 log) and Echerichia coli (9 log) (Oemcke, 1999; Buchholz et al., 1998).
The log number represents the number of 9’s in the percentage reduction. For example, a 2 log reduction means that 99% of the organisms originally present in the water have been inactivated. A 3 log reduction means that 99.9% have been inactivated, etc.
The capacity of the ultrasonic systems is also dependent on the power delivered. High power/ high intensity ultrasonic devices require less exposure time for mortality to occur thus allowing higher flow rates to be treated. Such ultrasonic systems can be used for ballasting and deballasting.
(cp. Sassi et al. 2005, p. 49)

Benefits of Ultrasonic Ballast Water Neutralization

• non-chemical
• environmental-friendly
• effective and efficient
• synergetic effects
• low maintenance
• safe and easy operation
• robust and reliable
• scalable to any size

Ultrasonic Equipment

Hielscher is specialized on the design and manufacturing of high power ultrasonic equipment of industrial grade for the installation in demanding environments. Dust & dirt, high humidities and rough environments does not damage the industrial ultrasonicators (UIP series). Those heavy duty devices are built for permanent operation (24h/ 7d). The cabinets come preconfigured and are easy to install and to start-up. The ultrasonic system only must be connected to the feed pipe from the ballast water tank (media supply) and the power supply.
Different sizes of ultrasonic devices with ultrasound power of 500W, 1kW, 1.5kW, 2kW, 4kW, 10kW and 16kW, which can be installed as single unit or as cluster, allow for the ideal configuration and processing capacity.
Talk to us about your processing volume! We will be glad to recommend you a suitable ultrasonic system for your process demands.

Synergies with other Ballast Water Treatments

Studies of combined treatment technologies have shown that ultrasound works very synergetic in combination with other ballast water disinfection methods, such as ozone, chlorination, UV-light, temperature or elevated pressures. Due to the easy installation and the low space requirements, the ultrasonic equipment is ideally suitable for an upgrade and improvement of already existing ballast water neutralization systems.
Talk to us about your processing environment! We will be glad to recommend you a suitable ultrasonic system to retrofit your onboard system.