© Inštitut za sanitarno inženirstvo, 2013.  Original scientific article New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologies Martina CVETKoVIĆ1, Boris KoMPARE2 ABsTRACT Bal ast water released from the cargo ships often acts as an inoculation mechanism for a large number of non-indigenous species that can have an important influence on marine ecosystem’s change and even devastation. The IMO’s “Convention for the Control and Management of Ships’ Bal ast Water and Sediments“ demands the establishment of bal ast water management system which should solve the question of uncontrol ed taking and the operations connected to bal ast water releasing. Also, it has been planned to complete the transition to bal ast water treatment system. The faculty team work on project which main aim is to examine and develop the principle of technology for bal ast water treatment, whose action is based on the use of the combination of filtering technology, hydrocyclone and cavitation. Until now, the project has proved the possibility of hydrodynamic cavitation appearance inside the hydrocyclone that has been an unexplored phenomenon Received: 30. 1. 2013 so far. The next step of the project is to prove hydrodynamic cavitation Accepted: 15. 11. 2013 effectiveness in a joint operation with hydrocyclone which should offer a solution for disabling and removing marine organisms from bal ast water. 1 Key words: Bal ast water, convention for the control and management of ships’ University of Ljubljana bal ast water and sediments, combination of filtering technology, hydrocyclone Interdisciplinary Doctoral Programme in Environmental protection, Jamova c. 2 and cavitation SI-1001 Ljubljana, POB 3422, Slovenia e-mail: martina_cvetkovic@yahoo.com 2 University of Ljubljana Faculty of Civil and Geodetic Engineering Jamova c. 2, SI-1001 Ljubljana POB 3422, Slovenia e-mail: boris.kompare@fgg.uni-lj.si * Corresponding author 48 International Journal of Sanitary Engineering Research Vol. 7  No. 1/2013 New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologi es  M. Cvetković, B. Kompare INTRoDUCTIoN Bal ast water from ships is considered the most important vector of non-indigenous organisms in aquatic ecosystems [1]. The transport of the world’s ship bal ast water stands at about 12 E9 t per year, and it is estimated that the ship’s bal ast tanks can transfer at least 10 000 dif- ferent species of organisms [2]. The bal ast water discharged from ships acts as an inoculating mecha- nism for non-indigenous species such as viruses and bacteria, Dinoflag- el ate, diatoms and other protists, zooplankton, benthic fish, as well as eggs, spores, seeds, cysts and larvae of various aquatic plants and or- ganisms. The bal ast water discharged In addition, zooplankton, especial y copepods, may be a carrier of path- from ships acts as an ogenic bacteria, such as Vibrio cholerae and Vibrio alginolyticus [2]. inoculating mechanism for In February 2004, International Maritime Organization (IMO) adopted a non-indigenous species such regulation – “Convention for the Control and Management of Ships’ as viruses and bacteria, Bal ast Water and Sediments (Bal ast Water Convention)”. It regulates Dinoflagel ate, diatoms and the methods of unloading ships’ bal ast water [3,7]. other protists, zooplankton, The convention refers to the reduction in the risk of non-indigenous spe- benthic fish, as well as eggs, cies from sea bal ast waters [4,5,6], and the main aim of the conventi- spores, seeds, cysts and on is to establish a Bal ast Water Management System. The Bal ast Wa- larvae of various aquatic ter Management System shall solve the problem of uncontrol ed intake plants and organisms. and operations related to bal ast water discharges in the period between 2009 and 2016. In the future, instead of the existing system of ship’s bal ast water exc- hange, a complete transition to a system of bal ast water treating is planned, which means that the ship’s bal ast water will be treated in accordance with standard rules of D-2 Bal ast Water Convention before they are discharged into the marine environment [4, 7, 8]. The treatment of bal ast D-2, a bal ast water quality standard, requires that in a cubic meter of water on ships is carried out discharged bal ast water should not be more than 10 surviving organ- by using the technologies isms that are equal as or greater than 50 µm, and in one mil iliter sho- that are integrated into the uld not be more than 10 surviving organisms whose dimensions are bal ast system from the between 10 and 50 µm [9]. intake through the tanks This standard also refers to the pathogens that represent a potential down to the discharge. threat to human health. The standard is governed by the general health standards and sets a maximum number of colony forming units (cfu) per hundred mil iliters of water for the three types of chosen indicator microbes, as fol ows [7, 8]: toxicogenic Vibrio cholerae (1 cfu/100 ml, or 1 cfu per gram of zooplanktonic sample, Escherichia coli (250 cfu/100 ml) and intestinal enterococci (100 cfu/100 ml). The treatment of bal ast water on ships is carried out by using the tech- nologies that are integrated into the bal ast system from the intake through the tanks down to the discharge. Thus the bal ast water treat- ment can be performed during intake or discharge at the inlet/outlet, in the pipes or in the bal ast tanks during navigation [10]. International Journal of Sanitary Engineering Research Vol. 7  No. 1/2013 49 M. Cvetković, B. Kompare  New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologies According to the IMO Convention, bal ast water treatment technologies should be [11, 12,13]: (1) safe, (2) environmental y friendly, (3) feasi- ble, (4) cost-effective, and (5) biological y effective. Very few of the existing bal ast water treatment technologies meet all the five criteria of the IMO Convention. These are, for example [7]: UV irradiation, Ultrasonic treatment, Ozonation, SeaKleen technology, De- oxygenation, Cavitation, etc. Stil , not one of these technologies is ful y satisfactory. Thus, we decided to combine interdisciplinary experience of our research group to possibly find a new and acceptable solution that will meet the mentioned criteria of the IMO Convention. The functioning of new technology is based on a combination of filtra- tion, hydrocyclones and cavitation. The aim of experiments is to exam- ine so far unexplored phenomenon of the appearance of hydrodynamic cavitation within the hydrocyclone. They will also try to prove the effec- tiveness of these combinations of technologies in removing marine or- ganisms from bal ast water. Very few of the existing Filtration is used as the first step and the primary procedure of bal ast bal ast water treatment water treatment in the new system (ship’s filter with a grate 8 * 8 mm in diameter). The filtration eliminates organisms and waste of larger di- technologies meet all the five mensions. Filtered water, with a help of the pumps, comes into the hy- criteria of the IMO drocyclone, which uses centrifugal force to separate particles and or- Convention. ganisms denser than the water density. They are eliminated through the lower exit of the hydrocyclone. Hydrocyclones are inertial devices that enable separation or concentra- tion of macrofluids as a suspension due to differences between the iner- tial forces that manage the movement of suspended substances in a liquid cargo [14]. The basic mechanism of hydrocyclone operation is the The functioning of new swirling flow, which influences the creation of centrifugal force [10, 15]. Sea water and organisms it contains do not have the same density. technology is based on a combination of filtration, Organisms and sediment with a density greater than the density of wa- hydrocyclones and cavitation. ter are suppressed by the swirling flow towards the wall of the hydrocy- clone. They will glide down the wall and at the end of the process they will be ejected through the bottom outlet. The phase with less density, i.e. purified bal ast water, remains in the central part, where, affected with the internal vortex, passes through the upper exit [16]. Figure 1 shows appearance and parts of the hydrocyclone device. 50 © Inštitut za sanitarno inženirstvo, 2013. New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologi es  M. Cvetković, B. Kompare Figure 1: Appearance and parts of the Clean hydrocyclone device, (Source: Lloyd’s water Register. Bal ast water treatment Vortex finder overflow technology Current status. London, 2010.) Inlet Typical trajectory of light particle Typical path of a larger heavier particle Underflow containing solids Hydrocyclones are considered to be a sustainable technology for the The main reason for the treatment of bal ast water because of the simplicity of use, operation development of and maintenance, low power consumption, the possibility of working hydrodynamic cavitation is a with a high water flow and resulting in a significant reduction of the variation of pressure in the problems associated with sedimentation in tanks. It is important to fluid flow, whereby vapor mention the fact that they do not have any impact on the health or sa- fety of the ship and its crew. cavities can be formed anywhere in the liquid flow. Cavitation represents the phenomenon of creation, growth and col apse of micro bubbles in a fluid. When a certain volume of fluid is exposed to a sufficiently low pressure, the fluid can burst and form a cavity (cavita- tion) [17]. Soon after this burst, the vapour col apses back into the fluid - in this phase very high pressures and temperatures may be achieved on a micro scale. The effects of hydrodynamic cavitation on chemical/physical processes and transformations are particularly investigated in the past decade [18]. The main reason for the development of hydrodynamic cavitation is a variation of pressure in the fluid flow, whereby vapor cavities can be formed anywhere in the liquid flow [19]. So far, hydrodynamic cavitation has been successful y applied for water disinfection, enzyme recovery and waste water treatment [20, 21]. Hy- drodynamic cavitation can be scaled up for operation on very large scale, especial y as required for bal ast water treatment [17]. International Journal of Sanitary Engineering Research Vol. 7  No. 1/2013 51 M. Cvetković, B. Kompare  New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologies Our idea is that hydrodynamic cavitation within the hydrocyclone should destroy the remaining organisms, i.e. the organisms whose density is equal as or less than the density of water and have escaped the cen- trifugal separation in the hydrocyclone. This step would also be the third (final) phase of operation of the new device for the bal ast water treatment. Until now, the use of these technologies for the bal ast water treatment has been relatively well known and researched, one by one. Also, the combination of filtration and hydrocyclone technology is well known, and the application of these technologies in removing marine organisms from bal ast water achieves high efficiency. But until now there are no reports on the proposed combination of filtration, hydrocyclone and hy- What is most important is drodynamic cavitation. the fact that the technologies What is most important is the fact that the technologies proved their proved their environmental environmental acceptability; they are safe and economical without acceptability; they are safe harmful chemical reactions or consequences to humans and environ- and economical without ment. harmful chemical reactions or Sedna’s system is one of the bal ast water treatment systems that uses consequences to humans and a combination of hydrocyclones and fine filtration (50 µm), together environment. with a chemical agent Paraclean Ocean [22]. This bal ast water trea- tment system has shown 98 % efficiency. The technologies which have also combined in their work the use of hydrocyclones and filtration, and which, at the same time, meet the re- gulation D-2 of the IMO Bal ast Water Convention are: ERMA FIRST S.A [23] (a combination of hydrocyclone, filtration and electrolytic cell Although successful for the extraction of chlorine to destroy the remaining organisms) and application of a combination Hamworthy Greenship B.V. (a combination of hydrocyclone, filtration and electrolytic chlorination) [24]. of filtration and hydrocyclones in the bal ast Although successful application of a combination of filtration and hydro- water treatment has been cyclones in the bal ast water treatment has been scientifical y proved up to now, the fundamental problem of existing technologies is the last scientifical y proved up to stage of technology operation. It has always involved the use of chemi- now, the fundamental cals which means the increase of risk for humans and environment. problem of existing technologies is the last stage Also, the use of chemicals further increases the overall cost of technolo- gy. There is a risk of corrosion or other harmful impacts on materials, of technology operation. and there is a need for specific additional training of the crew on han- dling the technology. The foreseen characteristics of our proposed new bal ast water treat- ment technology are: – No harmful effects on the environment – Cost of technology (low power consumption, the use of relatively cheap materials, ease of maintenance, ease of handling) – Low cost of purchase and device instal ation – Universality of application in relation to the size and purpose of the ship, and the capacity of bal ast tanks 52 © Inštitut za sanitarno inženirstvo, 2013. New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologi es  M. Cvetković, B. Kompare – Relatively short time of treatment with new technology – High percentage of efficiency in operating the technology – No risk of corrosion – Does not release toxic compounds and it is not hazardous in reacti- on with other substances – Adjustable technology in terms of space (does not take up a large area) METHoDs Description of laboratory pilot device The pilot device consisted of a chamber, integrated by the cylindrical and conical parts (Figure 1). The cylindrical part of the chamber was made of Plexiglas material due to experimental needs, while the other parts were made of steel. The hydrocyclone was connected to the cen- trifugal pump. The laboratory pilot device consisted of a hydrocyclone whose dimen- sions are shown in Table 1. Table 1: Dimensions of laboratory hydrocyclone Width 18 cm Length 36 cm Cone length 32 cm Cone angle 16o Pressure 0,5-2 bar The pilot device was constructed in such a manner that at the entrance of the vortex finder the phenomenon of hydrodynamic cavitation oc- curred. In order to achieve the best possible effect, in the first experi- ment, the entrance of the vortex finder, at the inlet section, had two conical mouths. A phenomenon of cavitation occurred at the “K” point of the cone. In the second cycle of testing, the nozzles with holes of various diame- ters were set up at the end of the vortex finder (photo 1), while the third cycle of research included experiments with cross-shaped additions to the nozzles with 6 or 8 partitions mounted at the end of the vortex finder or inside the vortex finder. The additions to vortex finder were used as mechanisms for calming down the vortex and increasing the longitudinal speed of the fluid which resulted in increased cavitation. In the experiments, two variations of vortex calming crosses were used – the first combination used in the experiments was a nozzle with a cross which was placed in the vortex finder of the hydrocyclone, while in the second variation, the cross was placed at the exit of the vortex finder as an inner extension of the vortex finder. The third variation used International Journal of Sanitary Engineering Research Vol. 7  No. 1/2013 53 M. Cvetković, B. Kompare  New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologies Figure 2: Schematic representation of the laboratory pilot device in the experiments implied a combination of the last two mentioned systems. Namely, the purpose of this segment of the experiment was to demon- strate the theoretical assumption that there was an increase of fluid ve- locity on the outer end of the vortex finder, which was caused by the Photo 1: placing of obstacles in different diameters, with the aim of creating rap- The appearance of nozzles for id constrictions. hydrocyclone vortex finder 54 © Inštitut za sanitarno inženirstvo, 2013. New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologi es  M. Cvetković, B. Kompare Therefore, the main goal was to increase the velocity of the fluid on the outer end of the vortex finder, with the aim of decreasing the pressure and, at the same time, creating the conditions for hydrodynamic cavita- tion occurrence. The inflow of water into the hydrocyclone had a rectangular cross sec- tion, positioned tangential y with respect to the outer surface of the hydrocyclone. The ball valve 3/4” at the bottom (bilge) control ed the flow of waste water (sediments and majority of organisms) on exiting the hydrocyclone and returning them back into the sea. The methods used and the further development of research At this stage of research, a pilot device (hydrocyclone) was constructed, and the behavior of water flow within the hydrocyclone was monitored. With the aim of development of hydrodynamic cavitation phenomenon on the vortex finder, the nozzles with 8,12,14,16 and 20 mm diameter were tested, and also one nozzle with 19 holes 4 mm in diameter, and a combination of cross-shaped additions to a nozzle with 6 or 8 com- partments that were placed at the end of or inside the vortex finder of the hydrocyclone. With every change of a nozzle, or a nozzle with addition, the fol owing factors were measured: flow rate, the pressure at the inlet ( p 1), the pressure before reduction ( p 2), the pressure at the entrance of the The inflow of water into the hydrocyclone ( p 3), the pressure of the hydrocyclone bilge ( p 4), the hydrocyclone had a pressure at the exit of the hydrocyclone ( p 5), the pressure on the outer rectangular cross section, rim of the hydrocyclone ( p 6), the pressure on the inner rim of the positioned tangential y with hydrocyclone after the occurrence of hydrodynamic cavitation ( p 7), the respect to the outer surface pressure at the point of hydrodynamic cavitation ( p 8), the velocity of of the hydrocyclone. water in the vortex finder, the speed of water when passing through the nozzle (theoretical value). In this phase, the hydrocyclone of corresponding characteristics was constructed, and the behavior of water flow within the hydrocyclone and the occurrence of phenomenon of the hydrodynamic cavitation and fluid motion trajectory were monitored, too. In the next step of the research, the samples of sea water will be taken and the properties, the content and the presence of certain organisms in the sample before and after the treatment with new technology should be checked. Further research will be divided into three groups: 1. Treatment of phytoplanktonic species; 2. Treatment of cysts and naupli 3. Treatment of zooplanktonic species The next phase of research should focus on checking whether the re- sults obtained during experiments meet the quality standards of bal ast water regulation D2, BWP (Bal ast Water Performance). International Journal of Sanitary Engineering Research Vol. 7  No. 1/2013 55 M. Cvetković, B. Kompare  New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologies The final step of the research of new bal ast water treatment technology will be a trial testing of the effectiveness of the technology on board. The objective of this phase of the project is to examine the previously tested technology in real conditions, when the technology is integrated on the ship. 3. REsULTs AND DIsCUssIoN The results of laboratory experiments with a pilot unit, where the noz- zles of different diameters as well as the nozzles with combination of additions were used, are shown in the Table 2. Experiments were per- formed at the air temperatures of 20-21 oC, and the water temperature 19.32 oC. An explanation for the nozzle and channel shapes: 0 - Normal nozzle with a hole 1 - Nozzle 0 with a cross for the vortex calming down 2 - Nozzle 0 with a cross for the vortex calming down positioned on the vortex finder 3 - Nozzle 1 with a cross for the vortex calming down positioned on the vortex finder The basic parameter that describes the process of cavitation is a cavita- tion number. It is calculated by the fol owing equation [26]: p p 0 v σ − = 1 2 V ρ 2 Where: ρ is the density of the fluid, p characteristic pressure, p is the 0 v Table 2: Results obtained from the vapor pressure of the liquid, V is a characteristic velocity of the flow. experiments on a laboratory pilot unit v nozzle Nozzle Form of Flow Q0 s nozzle v outlet pipe nozzles (teoret.) σ and (cavit. No.) ø [mm] channels [m3/h] [l/s] [x 10-3 m2] [m/s] (teoret.) [m/s] 12 0 2,77 0,769 0,113 6,803 0,367 10,187 12 2 2,72 0,755 0,113 6,680 0,361 8,144 12 3 2,62 0,727 0,113 6,434 0,348 10,899 14 0 4,57 1,269 0,154 8,246 0,607 4,927 14 2 4 1,111 0,154 7,217 0,531 5,177 14 3 5,96 1,655 0,154 10,754 0,791 2,658 16 0 4,55 1,263 0,201 6,286 0,604 12,142 16 1 5,55 1,541 0,201 7,667 0,737 5,087 16 2 5,4 1,5 0,201 7,460 0,717 6,468 16 3 8,88 2,46 0,201 12,268 1,179 2,305 20 1 8,92 2,477 0,314 7,887 1,184 4,539 19x 4 1 8,5 2,361 0,238 9,889 1,129 3,855 19x 4 3 8,34 2,316 0,238 9,702 1,107 3,973 56 © Inštitut za sanitarno inženirstvo, 2013. New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologi es  M. Cvetković, B. Kompare 14 12 10 8 Q0 (l/s) 6 σ (cavitation number) 4 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Figure 3: With the decrease of cavitation number σ the possibility of cavitation Dependence of the flow Q (l/s) on 0 occurrence increases. If σ decreases below 2.5, the cavitation will ap- cavitation number σ pear. As the mentioned number decreases and approaches number one, cavitation will be getting stronger and stronger. When cavitation number is greater than one, it means that the fluid is resistant to cavita- tion. When cavitation number is less than one, it means that fluid ener- gy (velocity head and pressure head at constriction) is being taken for the creation of vapor phase and hence cavitation [17]. Figure 2 shows the experimental results that describe the connection of hydrodynamic cavitation and flow in the pilot device. The graph shows the increasing flow in the laboratory hydrocyclone, which consequently influenced the decrease of cavitation number in the pipes (namely, with the increase of the flow rate, the velocity of fluid consequently increas- es, too). The results showed that the increase of the flow in the hydro- cyclone had influenced the increase of the possibility of cavitation oc- currence. As evident from Table 2, the best efficiency (ie the strongest cavitation) was achieved during the usage of the nozzle 16 mm in diameter, and the addition of a cross for the vortex calming down, that was placed on the vortex finder and had a flow rate of 2.47 l / s Figure 4: Dependence of cavitation number σ on the diameter of a nozzle 20 15 Hole size (mm) 10 σ (cavitation number) 5 0 1 2 3 4 5 6 7 8 9 10 International Journal of Sanitary Engineering Research Vol. 7  No. 1/2013 57 M. Cvetković, B. Kompare  New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologies Figure 3 shows the dependence of cavitation number on the diameter of the nozzle mounted on the vortex finder of hydrocyclone. As evident from the graph, the most powerful hydrodynamic cavitation occurred during the usage of a nozzle 16 mm in diameter and with an additional cross for the vortex calming down, set on the vortex finder. According to the results of the research, a very important effect on the occurrence of cavitation, other than a nozzle diameter, was the determi- nation of proper direction and calming down the water vortex which was executed by using the cross for calming down placed on the vortex finder. Table 3 and Figure 4 show the theoretical value of losses and pressure drop within a laboratory hydrocyclone for the fol owing flows: 1.39 l / s, Table 3: Energy losses and pressure drop as a function of changes in the flow of the pilot device Q0 d nozzle ∆ v2/2 g ∆ p (l/s) (x 10-2 m) m bar 1,388 2,5 -0,385 -3,78 E-2 1,388 2 -0,974 - 9,56 E-2 1,388 1,6 -2,412 -2,36 E-1 1,388 1,4 -4,130 -4,05 E-1 1,388 1,2 -7,671 -7,52 E-1 1,388 1,1 -10,875 -1,066 1,388 1 -15,932 -1,562 1,666 2,5 -0,555 -5,45 E-2 1,666 2 -1,403 -1,37 E-1 1,666 1,6 -3,473 -3,4 E-1 1,666 1,4 -5,948 -5,83 E-1 1,666 1,2 -11,047 -1,083 1,666 1,1 -15,66 -1,536 1,666 1 -22,942 -2,250 1,944 2,5 -0,756 -7,42 E-2 1,944 2 -1,910 -1,87 E-1 1,944 1,6 -4,727 -4,63 E-1 1,944 1,4 - 8,096 -7,94 E-1 1,944 1,2 -15,036 -1,475 1,944 1,1 -21,314 -2,091 1,944 1 -31,227 -3,063 2,222 2,5 -0,988 -9,69 E-2 2,222 2 -2,495 -2,44 E-1 2,222 1,6 -6,174 -6, 05 E-1 2,222 1,4 -10,574 -1,037 2,222 1,2 -19,639 -1,926 2,222 1,1 -27,839 -2,731 2,222 1 -40,787 -4,001 58 © Inštitut za sanitarno inženirstvo, 2013. New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologi es  M. Cvetković, B. Kompare 3 2 1 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 Q0 -1 delta p -2 -3 -4 -5 Figure 5: 1.67 l / s, 1.94 l / s, 2.22 l / s (in the case of experiments with these Dependence of pressure drop on flow flows, there was the strongest appearance of hydrodynamic cavitation). rates at different nozzle diameters The losses that occurred within the laboratory hydrocyclone increased proportional y with an increasing flow and with a reduction of the noz- zle’s diameter, as evident from the data given in Table 3. Thus, in these cases, for the smal est nozzle diameter of 0.01 m, (for all the tested flow cases samples), energy losses were the greatest in comparison with other measured flow rates and nozzle diameters. According to Borda Carnot - equation of losses and pressure drop, de- pend on the fol owing factors [25]: the density of medium and the squ- are of the change of speed in the system. According to Figure 4, where the pressure drop dependence on the flow rates of different diameters is shown, the largest pressure drops were noticed in the experiments with a nozzle which had the smal est diame- ter. This was directly connected with a flow increase. Namely, fluid ve- locity increases rapidly with the increase of flow and the reduction of the nozzle diameter. There was a sudden pressure drop which was ap- proaching vapor pressure, and it consequently led to the formation of cavitation. With the aim of the additional reduction of energy losses in further lab- oratory experiments, one of the possible changes could be the construc- tion change in the structure of the laboratory pilot device. It has been theoretical y proven that if the length of the cylindrical por- tion (part of plexia) is reduced, than subsequently, for the same used input factors, the losses in pilot hydrocyclone system will be signifi- cantly reduced. Table 4 shows a comparison of losses for the current length of 0.3 m for the cylindrical part of the laboratory hydrocyclone, and if the same was reduced to 0.12 m. Used flow rates were: 1.388 l / s, 1.666 l / s, 1.944 l / s, 2.222 l / s. International Journal of Sanitary Engineering Research Vol. 7  No. 1/2013 59 M. Cvetković, B. Kompare  New ballast water treatment system – combination of filtration, hydrocyclone and cavitation tehnologies 4. CoNCLUsIoN With the aim of achieving a high degree of efficiency in the removal of micro- and macro-organisms from sea water, reducing negative impacts on humans and environment, and satisfying economic criteria, the new bal ast water treatment technology has been designed. The functioning of new technology is based on the use of a combination of mechanical and physical bal ast water treatment systems, and the innovation which this technology has brought is the causing of the ap- pearance of otherwise undesirable phenomenon - hydrodynamic cavita- tion. It has been used for mechanical destruction of marine organisms that survived the previous step, hydrocyclonic treatment. Former investigations made on the laboratory hydrocyclone have shown the occurrence of hydrodynamic cavitation on the outer edge of the Vor- tex Finder. Experiments have confirmed the thesis of the interdepend- ence of hydrodynamic cavitation and other parameters such as flow, velocity in the pipe, and the speed in the hydrocyclone vortex finder. The occurrence of the strongest cavitation has been theoretical y and experimental y proved during the usage of an addition to hydrocyclone’s vortex finder in a shape of a nozzle 16 mm in diameter and a cross for Experiments have confirmed calming down placed on the outer edge of the vortex finder. During the mentioned process, flow rate was 2.47 l/s. the thesis of the interdependence of hydrodynamic cavitation and REFERENCEs other parameters such as [1] Flagel a, M., Abdul a, A. Ship Bal ast Water as a Main Vector of Marine flow, velocity in the pipe, and Introductions in the Mediterranean Sea. WMU Journal of Maritime Af- the speed in the fairs, 2005, 4 : 95–104 [2] Faimali, M., Garaventa, F., Chelossi, E., Piazza, V., Saracino, O.D., Rubi- hydrocyclone vortex finder. no, F., Mariottini G.L. and Pane, L. A new photodegradable molecule as a low impact bal ast water biocide: efficacy screening on marine organ- isms from different tropic levels. 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