Development of a technology based on hydrodynamically induced cavitation for the sanitization of ballast water. The goal is the complete killing of microorganisms and algae.
Currently, about 90% of the world's trade goods (ICS, 2018) are transported by ship. For the transport of trade goods, but especially for empty voyages, ships have to take in ballast water and release it again shortly before port call in order to regulate the trim, the heeling, the draught, the stability or the tensions of the ship (Umweltbundesamt, 2018).
Ballast water is used to pick up a wide variety of aquatic species and transport them around the world in ships, thus spreading them. WWF estimates that 7,000 marine and coastal species are shipped unnoticed through the oceans every day and are released into a new environment at the end of the journey with the discharge of the ballast water. However, more aggressive and rapidly reproducing species that find favorable living conditions can become invasive and compete with native flora and fauna. An additional lack of natural inhibitory biological factors, such as predators, pathogens, or parasites, can thus lead to the displacement of native species from their native ecosystem in the worst case. Thus, in addition to ecological damage, the introduction of these invasive species often entails a number of economic and health problems (WWF, 2009), (Umweltbundesamt, 2018). In addition to displacing native species, microorganisms in particular can also exchange genetic information (Baroni, 2013), so that resistance or pathogenic/toxic properties could spread more rapidly.
It is estimated that 200,000 to 50 million viruses are ingested into the ballast water tank with every milliliter of seawater (Ballastwatermanagement UK, 2017
This underscores the importance of stopping the introduction of non-native species, which is why, according to the recent decision of the Maritime Environment Protection Committee (MEPC) of the International Maritime Organization (IMO), all affected ships must be equipped with systems to treat their ballast water by 2024 at the latest (Umweltbundesamt, 2018).
ZeSys e.V. developed a technology for the hygienization of microorganisms in the ballast water of ships in order to prevent their spreading in non-native habitats when they are released in foreign regions. For this purpose, ZeSys e.V. designed and built a test rig based on the physical components of cavitation for the development of the technology and the functional model for the hygienization of microorganisms in ballast water. The ballast water to be treated is fed via a high-pressure system to special nozzles, each of which can then be used to generate a flexible hydrodynamic cavitation field. In this controllable cavitation field, pressures of several hundred to a thousand bar and temperatures of several thousand degrees Celsius are generated in the cavitation bubbles, which in combination with the resulting high shear forces lead to the destruction of microorganisms and algae. No chemical additives are used, and no ultraviolet light was integrated as part of the development, so that a purely physical high-pressure process is used.
The following results were obtained with the test bench:
The reduction from 6.8E+06 to 4.1E+03 kbE/ml corresponds to the killing of 99.94% of the microorganisms contained in the fluid.
The samples taken during the tests were analyzed both by PCR and microbiologically. The following are the PCR analysis results from a series of three tests:
"The degree of cell damage also affects our distinction between living and dead cells. We effectively block the DNA of severely damaged cells and no longer detect them in PCR. Slightly damaged cells may be less effectively blocked and therefore counted in PCR. In addition, PCR detects each cell and does not count cell clusters as one colony. Dividing cells are also counted as two cells. Therefore, PCR results are usually slightly higher (lower degradation values) than Mibi results." (C. Cordes, HS Bremerhaven)
The results are average results from multiple determinations.
Parallel to the tests with microorganisms, tests for algae destruction were carried out in cooperation with the partner Ankron. For this purpose, the prepared fluid mixed with algae was first pumped through the filter system developed by Ankron and then through the cavitation system. As a result, the following analysis result was determined (excerpt from the test protocol Ankron 10/2021 ):
"Table 3 shows the results of the cavitation. The effluent from the cavitation was analyzed for live zooplankton and algae. Furthermore, the biological activity of the algae was determined.
The best results for zooplankton and algae were obtained with the V0-5 setting. Zooplankton was absent from all samples and no remains could be found."
The developed technology can be used successfully in principle for the killing/inactivation of microorganisms as well as the destruction of algae and their combination in ballast water and similarly infested fluids within the scope of the laboratory scale design.
For larger flow rates, the laboratory design must be multiplied accordingly. The technology is unsuitable for use on large ships for ballast water sanitation because it is not yet possible to scale it up. Further developments of the technology are required for this purpose.
The pressure stages are to be adapted to the fluid/ingredient combination to be treated and thus to the fine nozzle design by empirical data determination.
In the design, the required absolute pressure in the cavitation field must be constantly guaranteed.
For the destruction of algae and their reformation, the two-stage process in the 105-110/6-10 bar gradation with the lower energy requirement, both in the laboratory configuration and in its upward scaling, is applicable.