We are developing a ballast water treatment system, under the sponsorship of The Nippon Foundation, to satisfy criteria related to ship's safety, operational complexity, capability to be installed on board ships, cost effectiveness and consequential environment impacts in addition to the effectiveness of treatment. Based on the results of extensive research, we believe a mechanical treatment system using a special pipe will match to the criteria.

　We have already given the presentation of the special pipe method at the GloBallast Symposium (March 2001 in London), at the MEPC 46 (April 2001 in London) and in the First International Conference on Ballast Water Management (November 2001 in Singapore). In this document, we report the effectiveness of the special pipe system as an improving treatment.

　

　

　The special pipe is modified to cause mechanical damage like shear stress to the organisms in the water. Organisms in the water are terminated or rendered harmless while ballasting or deballasting.

　The improved special pipe system described in this paper has a simpler mechanism and is more efficient than the pipe reported at MEPC 46, although the mechanisms of both pipes are the same in principle.

　

　

　We conducted the experiments with the treatment system installed on land, using natural seawater collected in a harbor area.

　The experiment flow is shown Fig.1. The inside diameter of the improved special pipe used for the experiments is 49.5 mm. The seawater flow rates were 170L/min, 260L/min and 350L/min in the experiments. The experiments were repeated three times at each speed.

　

　We evaluated the effectiveness of destroying aquatic organisms based on changes in the conditions of such organisms in seawater after one passage through the improved special pipe.

　The observed parameter used to evaluate effects on aquatic organisms was the number of normal individuals planktonic Crustaceans (Zooplankton). Examples of normal and terminated individuals are shown in Fig.2.

　

　

　We reported at MEPC 46 that one passage of natural seawater in the special pipe gave us an effectiveness of about 55％ of phytoplankton and about 65％ of planktonic Crustacean (zooplankton) in treated water at the outlet point of such a pipe.

　The improved special pipe system can terminate about 90％ of total planktonic Crustacean (zooplankton) in natural seawater (Fig.3c). This effectiveness was obtained using 60％ of the energy of the special pipe reported at MEPC 46 based on our experiment.

　In this way, the special pipe system was improved with respect to both the termination effect and the energy efficiency. Also, the improved special pipe system can terminate lager species (Fig.3a and c) and provide higher flow rates (see Fig.3a, b and c).

　We believe that the treatment effectiveness of the improved special pipe system could improve the termination efficiency for other phyto/zoo planktons, as both pipes could have the same treatment mechanism. Our experiments have also demonstrated that higher speeds in the pipe lead to higher treatment effectiveness.

　As this system is simple, it has the advantages of being able to be installed on board a ship, easy operation, cost effectiveness and others. Accordingly, we believe that mechanical treatment by using the special pipe is expected to become available and practical in near future, although still some matters must be solved such as reducing pressure loss and stuffing by the organisms and other substances in passing water in the pipe. The next stage of our research and development solves these subjects, and are to update the system in accordance with the standards to be developed in near future for aquatic organism treatment.