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FIELD OF THE INVENTION

The present invention refers to a system to be installed on floating units for removing microplastics from sea and ocean water, as well as to a method for operating the system.

STATE OF THE ART

The term “microplastics” is intended to mean small fragments of industrially produced polymeric materials. Although the definition is generic, by convention (adopted for example by the US National Oceanic and Atmospheric Administration, NOAA, and the European Chemicals Agency, ECHA) this term indicates plastic particles between 0.1 and 5000 micrometers in size (i.e. between 0.0001 and 5 millimeters).

Microplastics are then divided into primary, when they have the size indicated above already at the time of production, and secondary when they derive from fragmentation of larger plastic objects. Primary microplastics are mainly present in hygienic and cosmetic products (for example, in the form of abrasive microgranules in toothpastes and cosmetic creams), while secondary microplastics can derive for example from the wear of tires or clothes made of synthetic fabrics, or from the degradation of plastic bottles or bags.

These particles are considered to be among the main culprits of water pollution, in particular of seas and oceans: microplastics in personal care products, as well as those generated by washing clothes, reach the seas through household drains, while secondary microplastics may be produced on land and then be carried into marine waters by atmospheric agents (wind, or rain that carries particles into the sewer system) or they can form directly in the sea.

It is now recognized by the international scientific community that microplastics are a serious problem for sea and ocean environments because they are ingested by marine fauna, from the simplest species to fishes and large marine mammals, causing in the first place problems to this fauna (hormonal imbalances, alterations in growth and swimming skills ...) and contaminating the entire food chain up to man; for brevity purposes, the definition “sea water” in the remaining of the description is also intended to mean that of the oceans.

To solve the problem, or at least alleviate it, some studies have proposed the insertion of physical filters in land-based wastewater treatment plants. These filters are generally made up of metal mesh fixed to a frame arranged transversely with respect to a pipe of water to be filtered, and are characterized by the size of the openings, conventionally indicated with the “mesh” unit which corresponds to the number of meshes in the screen per linear inch.

Studies on this type of systems are reported, for example, in the articles “Solutions to microplastic pollution - Removal of microplastics from wastewater effluent with advanced wastewater treatment technologies”, J. Talvitie et al., Water Res., vol. 123, October 2017, pages 401-407, and “Removal of > 10 pm microplastic particles from treated wastewater by a disc filter”, M. Simon et al., Water (open access journal) 2019, 11(9), 1935.

A problem with terrestrial systems of this type is that they cannot intervene on microplastics released directly into the sea (primary) or formed in the sea due to wear and degradation of macroscopic waste (secondary), nor on the huge amount of microplastics already present in seas and oceans.

The object of the present invention is to provide a system capable of removing microplastics from sea water to be installed on floating units, and the method for using the system.

SUMMARY OF THE INVENTION

These objects are achieved through the present invention, which in its first aspect relates to a system, to be installed on floating units, for removing microplastics from sea water, comprising:

- a first connecting line between a first opening on a wall of the floating unit for loading sea water, and a second opening on the wall of the floating unit for discharging water into the sea;

- on said first line, in sequence from said first opening to said second opening, a first shut-off valve, a first filter, a first pump for loading sea water, a second shut-off valve, a first non-return valve, at least one ballast tank, a third shut off valve, a second pump for discharging into the sea water from the at least one ballast tank, a third non-return valve and a fourth shut-off valve; characterized in that it further comprises:

- on said first line in sequence from said first opening to said second opening, between said first non-return valve and said at least one ballast tank, a water filtration device for removing microplastics and a second non-return valve;

- a second line connecting said water filtration device for removing microplastics to said second opening on which, in sequence from said water filtration device to said second opening, a tank for the temporary storage of microplastics and a fourth non-return valve are present, wherein said tank for the temporary storage of microplastics is equipped, in correspondence of its outlet opening towards said second opening, with a filter element having hole sizes equal to or smaller than those of the filter elements present in said water filtration device;

- a third line between said water filtration device for removing microplastics and said at least one ballast tank, on which a third pump is present.

In its second aspect, the invention relates to the method for operating the system described above to remove microplastics from sea water and store them in a temporary tank until they are disposed of in safe conditions.

BRIEF DESCRIPTION OF THE FIGURES - Fig. 1 schematically represents the system of the invention in a first embodiment thereof;

- Fig. 2 schematically represents the system of the invention in a second embodiment thereof which is specific for ships;

- Fig. 3 shows a sectional view of a possible seawater filtration device to be used in the systems of Figs. 1 or 2;

- Fig. 4 shows a sectional view of a preferred device for filtering sea water to be used in the systems of Figs. 1 or 2.

DETAILED DESCRIPTION OF THE INVENTION

In its first aspect, the invention relates to the system described above in its essential components, to be installed on floating units, which allows the removal of microplastics from seawater.

In the present description and in the claims, the term “floating units” is intended to mean both units used for transport according to the Navigation Code, i.e. self- propelled vessels, and thus ships of various sizes, and floating structures not endowed with self-propulsion such as off-shore platforms.

Furthermore, in the description and in the claims, reference is made to “at least one ballast tank”, but usually in floating units (being these ships or platforms) there are multiple ballast tanks, symmetrically arranged in the unit, intended for filling with sea water called ballast, i.e. the amount of weight that increases the weight of the unit itself; in the case of ships, this has the purpose of conferring a better aptitude for navigation and greater safety in the absence of the load weight or when the load weight is reduced. The system of the invention does not require a deep change of the current construction methods for floating units; rather, the characterizing part described above, formed by the filter for microplastics, by the tank for temporary storage of the same, and by a filter washing system in counter-current (in addition to the water lines and the necessary valves and pumps), can be integrated in retrofitting mode in the seawater circulation systems already present on said floating units for loading and emptying at least one (but usually more than one) ballast tank.

Fig. 1 schematically shows a possible seawater treatment system of the invention. The arrows in the figure indicate the direction of the water flows in the system.

The system, 100, comprises a first line 101 , a second line 116 and a third line

119.

The first line, 101 , connects a first opening (102) on a wall of the floating unit to a second opening (103) on a wall of the floating unit; the first opening is needed for loading sea water to form a ballast, while the second opening allows the ballast water to be discharged into the sea. On this first line 101 , there are purpose functional elements, and elements which ensure that the flow of water can only take place in the direction from the first opening 102 to the second opening 103. These elements are, in sequence from the first to the second opening, a first shut-off valve 104, a first filter 105, a first pump 106 for loading sea water, a second shut-off valve 107, a first non-return valve 108, a water filtration device 109 for removing microplastics, a second non-return valve 110, at least one ballast tank 111 , a third shut-off valve 112, a second pump 113 for discharging the at least one ballast tank, a third non-return valve 114, and a fourth shut-off valve 115. On the first line 101 there are also some of the elements that characterize the present invention, not necessary for the function of loading and unloading the ballast water and not present in known systems; these additional elements, arranged between the first non-return valve 108 and the at least one ballast tank 111 , are a water filtration device 109 for removing microplastics and a second non-return valve 110.

The second line, 116, connects the filtration device 109 to said second opening 103. On line 116 there are, in sequence from the filtration device 109 to the second opening 103, a tank 117 for the temporary storage of microplastics and a fourth non return valve 118. As described below, on this second line there may also be a further shut-off valve (not shown in Fig. 1), depending on the type of filtration device 109 adopted in the system.

Finally, the third line 119 connects the filtration device 109 to said at least one ballast tank 111 ; in this third line, the water moves counter-flow with respect to the direction of the flow in line 101 ; the direction of the water flow in the third line 119 is ensured by a third pump 120.

As mentioned, most of the elements on line 101 are already present in traditional ballast water loading systems, and do not require a detailed description. In short, the shut-off valves 104, 107, 112 and 115 allow the system or parts thereof to be closed and isolated from sea water when necessary; the non-return valves 108 and 114 are safety elements that ensure the direction of the water flow in the system in the event of malfunctions of other system elements; the filter 105 has relatively large openings, generally of between 3 and 12 mm, to avoid constituting an excessive obstacle to water loading, and has the purpose of preventing the entry of higher marine animals, algae or large debris into the system; the first pump 106 is the essential element for loading the ballast water; and the second pump, 113, has the purpose of facilitating the discharge of water from the at least one ballast tank 111.

In the case of ships, on line 101 there is also a seawater bio-treatment system to eliminate microorganisms from it. The reason for the presence of this additional system element is that the loading of sea water in a first geographical area, and its discharge in a different area, generates the risk of biological contamination due to the transport of microorganisms typical of an ecosystem into a different one. To remedy this problem, the “International Convention for the Control and Management of Ships’ Ballast Water and Sediments” adopted by the IMO (International Maritime Organization) in February 2004 and entered into force in September 2017, obliges ships that operate on transoceanic routes to be equipped with a biological treatment system for the loaded water, aimed at extinguishing the microorganisms loaded on the ship with the ballast water.

The seawater bio-treatment device can be of various types and based on chemical, electrochemical or physical treatment principles. Possible chemical processes consist in adding into the device chlorine dioxide, CIO2, which has a superior biocidal action compared to that of simple chlorine and is less corrosive than the latter in water, or ozonation, which consists in adding ozone, a powerful oxidant with biocidal action, to the water (ozone can be produced in special devices, called ozonizers, in which a cold plasma is formed determining the formation of the gas starting from atmospheric oxygen). The electrochemical processes may consist of electrocatalysis or electrolysis of sea water which generates gaseous chlorine in situ. Finally, a seawater bio-treatment device can work thanks to lamps emitting ultraviolet radiation, which are also known to have a biocidal action.

A system of the invention for use on ships, comprising a seawater bio treatment device, is schematically shown in Fig. 2; the system, 200, is similar to that of Fig. 1 (in Figs. 1 and 2 the same number corresponds to an identical element), but comprises the bio-treatment device 201 positioned between the shut-off valve 107 and the non-return valve 108.

According to the present invention, the system for the removal and temporary storage of microplastics, consisting of the second line 116, the third line 119, and the elements present on these, is added to the known elements described above and already present or provided on floating units.

In particular, the characteristic elements of the invention are the water filtration device 109 for removing microplastics, inserted on the line 101 and from which the line 116 starts, on which there are also the tank 117 for the temporary storage of microplastics and a fourth non-return valve 118; and the third pump 120 on the third line 119.

Fig. 3 schematically and sectionally illustrates a water filtration device 300 for use in the invention in its simplest possible configuration; this configuration is essentially described to illustrate the filtering device operating principle. The device, 300, is divided into two compartments, 301 and 302, by at least one filter element 303; the element 303 comprises a mesh (generally metallic) fixed to a frame connected to the internal walls of the device 300. The microplastics entering the device through the flow of water arriving from the line 101 are retained in compartment 301 , until they are discharged from this compartment through the opening of the shut-off valve 304 (the valve 304 is not shown in Figs. 1 and 2 as it is required only when this simple form of filtration device is used); the water purified from microplastics passes through the filter element 303, and from compartment

302 it continues along line 101 towards the ballast tank 111 (the latter is not shown in the figure).

The tank 117 for the temporary storage of microplastics receives the microplastics from compartment 301 through line 116 during the cleaning of filter

303 (as described below with reference to the method of the invention). In correspondence with the outlet opening of the tank 117 there is a filter element 305 with hole sizes equal to or smaller than those of filter 303, so that the water in the tank 117 can flow towards the drain opening 103, but the microplastics (indicated in the figure with M) are retained in the same tank.

Fig. 4 schematically and sectionally illustrates a water filtration device for use in the invention in a preferred configuration, which increases the area of the filtering surface, and thus the efficiency of the device, for the same volume. The device, 400, has a cylindrical geometry and contains filter elements 403, 403’, ..., dividing its internal volume into first compartments 401 , 40T, 401”, 40T” and a second compartment 402.

The line 101 , which feeds the water containing microplastics inside the device, has openings in correspondence with the first compartments 401 , 40T, 401 ”, 401 in the outgoing portion towards the ballast tank, the line 101 is in communication with the second compartment 402. A line 119 in turn is in fluid communication with the second compartment 402 through branches 404, 404’, ... of said line, to which sprinklers 405, 405’, 405”,... are connected; for simplicity, only one sprinkler for each branch is shown in the figure, but the number of sprinklers connected to each branch of type 404 could be higher (for example, from three to five). Inside line 101 there is a manifold 406 open at the top for washing water containing microplastics (the top opening is indicated by the dotted line in the figure); the manifold 406 is part of the line 116 outgoing from the device 400, connected to the tank 117.

Systems and devices of the invention have been described above with reference to Figs. 1 , 2, 3 and 4 by way of example, but it will be apparent to the person skilled in the art that structural changes can be made to these systems that do not alter their operation, and are to be considered as included in the invention.

Only to provide some examples of possible modifications, in the system represented in Fig. 1 the positions of some valves, for example the valves 114, 115 could be inverted, and the valve 118 could be positioned upstream of the tank 117; and the filtration device 400 could contain a different number of first compartments of type 401 , for example from 2 to 15.

In its second aspect, the invention relates to the method for removing microplastics from sea water and storing them in tank 117 until they are safely discharged. With reference to Figs. 1 and 2, according to the normal operation of the ballast system of a floating unit (a ship in the specific case of Fig. 2), by opening the shut-off valve 104 and operating the pump 106, sea water is loaded through the opening 102; the water is filtered by the filter 105 to remove superior animals and large debris and is sent along the line 101 to fill the ballast tank 111. When necessary, the water is discharged from the ballast tank 111 into the sea through the opening 103 by opening the shut-off valves 112 and 115, and by operating the pump 113.

The microplastics filtration device (109; 300; 400) is positioned on the line 101 , preventing microplastics from reaching the ballast tank 111 and therefore from being discharged back into the sea. From the filtration device, through its counter-current washing, the microplastics are transferred, in the manner described in detail below, to the temporary storage tank 117. The tank 117 can be emptied, also manually, when it contains excessive amounts of microplastics or, in the case of ships, also whenever the ship is anchored in a harbor.

Flow the device of filtration of microplastics is cleaned from the same depends on its specific configuration. In the simplest possible case, the device, 300, comprises only two compartments 301 and 302 separated by a filter element 303. Over time, the filter element 303 becomes clogged with microplastics, and the flow of water through the same is hindered, resulting in operating problems of the ballast system; the filter clogging condition can be controlled in an automated way, for example, by connecting two manometers to the two compartments 301 and 302 and monitoring the pressure drop at both ends of the filter continuously or at predetermined time intervals. When the filter element 303 is found to be clogged, it can be regenerated by counter-current washing. For this purpose, the pump 120, which pushes water from the ballast tank 111 towards the compartment 302, is actuated; water passes through the filter element 303 in the direction from compartment 302 to 301 , displacing the microplastics adhering to the surface of the filter element 303 facing the compartment 301 ; the non-return valve 108 prevents the flow of water from returning into line 101 in the direction of the first opening 102. By opening the shut off valve 304, the water containing the microplastics removed from the filter is directed towards the tank 117; inside the latter, the microplastics are blocked by the filter element 305, while the water can flow along the line 116 towards the discharge opening 103.

In the case of the filtering device 400, the water follows the direction indicated by the arrows in Fig. 4, and therefore flows (or can flow) simultaneously in the ballast tank loading direction and in the filter washing direction (counter-flow with respect to the loading direction).

In this case, the water to be treated enters the device through the line 101 , reaches the lower portion of the compartments 401 , 401 ’, 401 ”, 401 and from there it can pass into compartment 402 only through the filter elements 403 , 403’,... , which retain the microplastics. The water passed into compartment 402 reaches the ballast tank through the line 101 at the outlet.

The device 400 operates so that the level of water inside it does not exceed (or only slightly exceeds) its axis, so that the upper portion of the compartments 401 , 40T, 401”, 40T” and of the filter elements 403, 403’,... , as well as the upper opening of the manifold 406, are not immersed in water.

The surfaces of the filter elements (403, 403’, ...) facing the compartments 401 , 401’, 401”, 401’” must be periodically or continuously cleaned of microplastics. Cleaning is carried out by rotating the filter elements around their axis, so as to bring the portion thereof that is initially in the lower portion of the device in the upper portion of the same, in correspondence with the sprayers 405, 405’, 405”, ... which receive the washing water through the line 119 and the branches 404, 404’, ...

The water sprayed on the surfaces of the filter elements 403, 403’, ... (represented in Fig. 4 as element 407), removes the microplastics from these and carries them, from the upper portion of compartments 401, 40T, 401”, 40T”, along the direction of the arrows towards the upper opening of the manifold 406, and from here it flows along the line 116 towards the tank 117. Also in this case, as in the case illustrated with reference to Fig. 3, the washing takes place in counter-flow.

The washing of the surfaces of the filter elements 403, 403’, ... by rotation around their axis can take place periodically, when an excessive clogging of the same is noted (for example, by observing an excessive water rise in the device 400), or in a continuous way.

The tank 117 must be periodically emptied of the accumulated microplastics; this could be done through one or more hatches arranged on the upper and/or lower portion of the tank itself (not shown in Fig. 3), or with other methods which will be apparent to the person skilled in the art. The system and method of the invention therefore allow the removal of microplastics from sea water as part of the normal operation of the ballast system of floating units.