The project "Research and Development of the Special Pipe System for Ballast Water Treatment" conducted by the Japan Association of Marine Safety under the sponsorship by the Nippon Foundation has two components: 1) improvement the special pipe system to achieve better effectiveness in the termination of zooplankton and phytoplankton, and 2) development of the procedure and standard for evaluation of the effectiveness. This paper describes the first component, and the second one is also explained in another article recorded in the same proceedings.

　

　

The instrument designed in the special pipe system uses the options that can be categorized in a mechanical treatment, because it applies shear stress and cavitations generated in the instrument for termination of organisms in ballast water. During the development stage of the prototype pipe system, which was reported verbally at the 1st GloBallast Symposium held more than two years before, injection of ozone into ballast water before a passage of the pipe was tried to increase termination efficacy. But mixture of such chemicals has not been applied to the new system, mostly because of the difficulty in the installation of an instrument for provision of chemicals to the system.

　

　

The project has three phases, commencing from April 1999.

　

　

　

The objective of this study is to develop a ballast water treatment system to terminate and eliminate harmful aquatic organisms contaminated in ballast water with special attention to criteria related to safety of ship and crew, practicability in terms of operational complexity and installation on board ships, cost effectiveness, and consequential environment impacts in addition to the effectiveness of treatment.

　

　

The prototype special pipe system was designed to use shear stress to terminate planktonic organisms. The potential was high, as reported at MEPC 44 in 2000, and verbally at the 1 International Ballast Water Treatment Symposium (2001, London) and at the First International Conference on Ballast Water Management (2001, Singapore). This structure was, however, not suitable for practical use, because its pressure loss in passing water was high and needed higher pressure in a pipe with a larger diameter. The higher pressure could not cause higher damage to organisms in the pipe.

　

Then the special pipe was re-designed with a unit generating shear stress and cavitations. Comparison of effectiveness between the former and the developed special pipe systems was made to ascertain the higher level of effect on marine organisms and the smaller pressure loss in the case of developed one.

　

　

The analysis of the effectiveness of the prototype special pipe system was conducted in laboratory with and without adding ozone produced by an ozonizer using natural seawater collected in a harbor area at Imari Bay in Kyushu Island, western Japan.

　

The inner diameter of the special pipe used for the experiments was 40 mm. The seawater flow rate was 20 m³/hr. The concentration of ozone as oxidant in sea water was 1mg/L, when injected.

　

　

Termination efficacy of the improved special pipe system was analyzed by using the system installed in the harbor with natural seawater taken in at the harbor area at Imari Bay in Kyushu Island, western Japan. The experiment flow is shown in the figure 1. Figure 2 shows the appearance of the main part of the improved special pipe. The inner diameter of the pipe used for the experiments is 100 mm. Two different flow rates of seawater, 115 m³/hr and 150 m³/hr were applied at the experiments.

　

In case of 115 m³/hr flow rate, the quantification of live phytoplankton and zooplankton was carried out 5 times using method described below, and an average individual number of live organisms was calculated by subdividing all organisms into 4 different size range groups; smaller than 20 um, between 20 and 50 um, between 50 and 100 um, and larger than 100 um. Total individual number of phytoplankton and zooplankton was also calculated from the data of these four subgroups.

　

In case of 150 m³/hr flow rate, only one data set has been available for the moment, as more experiments are now in planning. Numbers of live organisms were counted separately for those smaller and larger than 20 um by the method described below.

　

　

The effectiveness of the special pipes was measured by the termination rate of phytoplankton and zooplankton, comparing the number of live organisms in initial seawater and treated seawater after passage of the pipes. Dead or live of the organisms in the water samples was judged based on the change of appearance, i.e. shape and color, of individual phytoplankton and zooplankton. Examples of the normal and terminated phytoplankton and zooplankton are shown in Figure 3. Quantification was made by counting live organisms in one ml portion of water samples taken onto a Sedgewick-Rafter chamber under a regular compound microscope.

　

Preparation of seawaters samples for microscopic observation was different between organisms larger than 20 um and the rest (smaller than that). The former was observed after concentrating the seawater samples 1,000 times using 20 um plankton net cloth, because individual number larger than 20um was not high. On the other hand, the latter was observed without concentration.

　

　

Termination efficacy of the improved special pipe system in relation to flow rate was analyzed by using the system installed at Imari Bay in Kyushu Island, western Japan. The inner diameter of the pipe used for the experiments is 50 mm. Termination rate was calculated using zooplankton larger than 20 um as test organisms, and quantification of individual zooplankton was made three times at three flow rate, 10.5, 16 and 21 m³/hr.

　

　

　

Termination rates of phytoplankton and zooplankton with and without injection of ozone are shown in Table 1. One-passage treatment gave an effectiveness of about 55% of phytoplankton and about 65% of zooplankton and they increased to about 99 and 89%, respectively, by injecting ozone.

　

　

The improved special pipe system can terminate about 70 and 95 % of all phytoplankton and zooplankton, respectively, in natural seawater in the case of one-passage treatment at the seawater flow rates 115 m³/hr (Table 1). This effectiveness was obtained using 60% of the energy of the prototype pipe. This effectiveness increased about 80 and 100 %, respectively, by two-times passage treatment, and furthermore, they reached 85 and 100 %, respectively, at flow rates 150m³/hr. (Table 1).

　

　

Table 2 and 3 show the details of the result with size fractions obtained at 115 and 150 m³/hr, respectively. These results indicates that larger phytoplankton and smaller zooplankton are more effectively terminated than the others

　

　

　

　

　

　

　

　

Figure 4 shows the termination rate of zooplankton in response to flow rates in the pipe. It is obvious that the higher flow rate produced higher treatment effectiveness.

　

　

The main part of the system can be installed as a part of ballast water intake line or discharge line. The size is 1m long and 0.5m height in case of pipe having the inner diameter 100 mm. Figure 5 shows the model prepared for on board ship test which will be practiced in the latter half of this year 2003. The installation cost of the system could be estimated as 100,000 US$ per a unit, and the running cost could be 0.01 US$/ton.

　

　

Termination efficacy of the improved special pipe system is very high. Only one time passage through the pipe kills more than 84 % of phytoplankton and almost 100 % of zooplankton (Table 1 and 3). As expected from the data using a pipe of inner diameter 50 mm shown in the Figure 4, it is not difficult to have higher termination rate in the pipe of 100 mm inner diameter, if faster flow speed can be applied. Multiple passage through the pipe, or application of the pipe system for both intake and discharging waters can produce higher termination rate.

　

The mechanical treatment by using the improved special pipe system may be one of the treatment options by its practicability in terms of easiness in installation on board a ship, safe in operation and maintenance and cost performance, in addition to effectiveness in termination of organisms contaminated in ballast water. The authors have a plan of on board test in this year, and expect that the system become available and practical in quite near future.