Method and device for desalination of seawater by reverse osmosis

Abstract

A method for desalinating seawater and a device for carrying it out, comprising the steps of providing a reverse osmosis module fluidly connected to the upper end of a marine water body at a depth within the water body, with i as an element of the natural numbers and i>0, wherein the reverse osmosis module comprises a cavity with a process water chamber having an inlet and an outlet, and a permeate water chamber, which are separated from one another by an osmosis membrane filter; providing an outlet manifold fluidly connected to the outlet of the process water chamber at an outlet depth within the water body and having an outlet directed towards the ambient water, and discharging the permeate water from the permeate water chamber;wherein a process water flow is formed from the inlet of the process water chamber to its outlet, which has a hydrostatic process water pressure p1 in the reverse osmosis module built up by the depth h1 of the reverse osmosis module in the water body;

Description

The invention relates to an energy-efficient, wear-reducing and environmentally friendly method for desalinating water of a marine body of water by means of reverse osmosis and to a device developed for this purpose which also helps to reduce the area requirement of such installations, typically installed close to the coast.Marine waters are generally referred to as waters belonging to the sea, i.e. being part of a sea or being connected thereto in so far that the water has seawater quality, in particular a salt content which is unacceptably high for service water and / or drinking water.Seawater desalting plants (MWS plants) supply an increasing proportion of the world population with water and in the meantime form an indispensable constituent of urban infrastructures in dry areas, which is increasingly being developed. At the same time, MWS plants are in criticism for various reasons:The plants based on reverse osmosis in most practical cases work energy intensive. This even forces operators to erect MWS plants as much as possible near power plants to minimize additional costs of grid construction and loading. The concentrated wastewaters from MWS plants are returned to the sea close to the coast in practice. This entails ecological risks, on the one hand because of the high salt concentration and the chemicals added to the salt water stream during water recovery, but also because salt water chemically attacks pumps and other metallic technical equipment, as a result of which the reaction products likewise accumulate in the waste water.The technical devices exposed to salt water, in particular the high-pressure pumping technique and valves, are subject to high corrosion-related wear. The construction of MWS installations which leads to high area consumption close to the coastline causes conflicts of interest with other uses. This also applies to energy-saving concepts which derive the energy for water extraction, for example from the movement of water in the vicinity of the coast.Within an MWS plant, salt water is taken from an underground water body (sea, ocean). This is brought to a high pressure, prefiltered and concentrated in the course of reverse osmosis. The substantial portion of the energy to be expended in seawater desalting via reverse osmosis is attributable to the generation of this salt water under high pressure, this high pressure being necessary in order to be able to press a portion of the salt water through the osmotic membrane filters against its osmotic potential. This initially necessary pressure of about 20 bar must reach up to 80 bar with increasing concentration of the salt water flowing past the osmotic membrane filters in order to overcome its growing osmotic potential, in the process achieving a sufficient water flow (permeation) through the osmotic membrane filters and thus generating the desired mass flow of demineralized water.To explain the invention, the prefiltered salt water is referred to below as permeate water and the water permeating into a separate collecting container, the permeate water space, is referred to below as permeate water.Currently operated reverse osmosis systems achieve a separation degree of about 0.5. This means that about 1 l of demineralized water can be obtained from 2 l of salt water, which is now optionally treated even further in order to achieve drinking water quality, for example.The object of the invention is to provide a method for desalinating seawater by means of reverse osmosis and a corresponding device for carrying out the method, which make it possible to design desalinate seawater in a more energy-saving and environmentally compatible manner than is possible in conventional MWS plants.The object is achieved on the process side by the features of independent claim 1 and on the device side by the features of independent claim 6. Further expedient embodiments of the invention are the subject matter of the dependent claims.To achieve the object, a method for desalinating seawater is proposed, comprising the steps of◯ Providing at least one reverse osmosis module fluidly connected to the upper end of a marine body of water at a depth h i, with i as element of natural numbers and i>0, inside the body of water, wherein the reverse osmosis module comprises an outwardly encapsulated cavity with a process water space having an inlet and an outlet and a permeate water space separated from each other by at least one osmotic membrane filter;a Providing an outlet distributor which is fluidically connected to the outlet of the process water space of the reverse osmosis module at an outlet depth h within the body of water, wherein the outlet distributor has an outlet which is directed towards the surrounding water;a Providing an outlet distributor which is fluidically connected to the outlet of the process water space of the reverse osmosis module at an outlet depth h within the body of water, wherein the outlet distributor has an outlet which is directed towards the surrounding water;◯ prefiltration of a part of the body of water flowing into the process water chamber before its contact with the osmotic membrane filter, for forming process water;i positioning the reverse osmosis module in the body of water at a depth h in such a way that a part of the body of water flows through the inlet of the process water space to the outlet thereof, for forming a process water stream in the process water space;◯ forming a hydrostatic process water pressure p i in the process water space of the reverse osmosis module by setting a depth h i of the at least one reverse osmosis module in the body of water in such a way that a pressure gradient is formed from the process water space to the permeate water space and consequently at least a part of the process water is pressed through the osmosis membrane filter along the pressure gradient; anddraining permeate water from the permeate water space.According to the invention, a water stream of seawater of the body of water, referred to below as process water stream, is formed from the inlet of the process water space to the outlet of the process water space, which water stream has a hydrostatic process water pressure p i in the reverse osmosis module, which hydrostatic process water pressure p is built up by the depth h i of the at least one reverse osmosis module in the body of water. The usable process water pressure p i is obviously limited to a plant-specific, determinable maximum value, up to which the components of the plant are protected from overloading.The method is based on a system concept in which functional modules are positioned at / near the surface of the body of water or at different depths within the body of water and are fluidically linked to one another by means of pipe or hose lines and necessary connecting means.A reverse osmosis module is already sufficient for implementing the invention. For a better illustration of the operating principle, the invention is described on the basis of a plurality of reverse osmosis modules which-unless otherwise expressly described-are arranged in series.Various functional modules are listed below by way of example, wherein not all of the functional modules listed below are absolutely necessary for achieving the object of the invention: Reverse osmosis modules including, if appropriate, buoyancy bodies present Outlet Distributor pumpand in some embodiments➢ Processing Platform Processing and Control Modules on the Processing Platform prefiltration modules and / or prefiltration devices formed in other components or in fluidic connections.The initialization of the multiwater desalting can comprise the following method steps:➢ of the following components in the body of water i) of the processing platform close to the water surface and optionally of prefiltration modules for prefiltration of water to be desalted, ii) of the reverse osmosis modules in deeper water layers (depths h i, where i=1,2,3,... ) of the body of water and iii) of the outlet distributors at again greater water depths h a, where a=I,II,III,... for discharge of process water via (optionally) directable nozzles into the body of water and fluidic connection of the modules carrying the water flow, wherein prefiltration modules are fluidically connected to the process water-side inlets of the reverse osmosis modules, the process water-side outlets of these are connected to the process water-side inlets of possibly further reverse osmosis modules positioned deeper in the body of water or the outlet distributors, and fluidic connection of the permeate water-side inlets and outlets of the respective reverse osmosis modules to the processing and control modules on the processing platform with pipe or hose lines in order to guide the permeate water stream and optionally a gas or air stream.The desalting of seawater itself is now carried out in a plurality of process steps, wherein not all of the steps listed below are absolutely necessary to achieve the object of the invention and fresh water production can in principle also be realized with only one of the reverse osmosis modules:➢ pre-filtration of seawater, for example of seawater close to the surface, by means of a pre-filtration module or a pre-filtration device for providing the process water, andi supplying the process water on the process water space side to the osmosis membrane filter of the at least one reverse osmosis module positioned at the depths h, and adjusting differential pressures between their process and permeate water spaces separated from one another by osmotic membrane filters by conveying permeate water from the permeate water spaces with pressurized water pumps integrated into the reverse osmosis modules, which results ini filtration of further process water present under the hydrostatic pressures p in the process spaces of the respective reverse osmosis modules through the osmotic membrane filters in their permeate water spaces, as long as the permeate water pressures in these are less than the differences between the hydrostatic process water pressures minus the salinity-dependent osmotic pressures, and demand-dependent modulation of the feed rates of permeate waters from the respective reverse osmosis modules, and Continuous replacement of the concentrated process waters by less concentrated process waters by the process water spaces of the reverse osmosis modules being supplied via pipe or hose connection to the outlet distributors arranged deeper in the body of water and there are discharged directed via oriented / orientable outlet nozzles into the surrounded body of water, and lifting the permeate waters from the respective permeate water spaces to the processing and control modules present, for example, on the processing platform by means of pressurized water pumps integrated in / on the reverse osmosis modules, which at least partially have to overcome the respective pressure levels up to the processing modules, and detection and, if appropriate, control of the hydrostatic pressures in the process water spaces of the reverse osmosis modules by lowering or raising the reverse osmosis modules in the body of water, and detection and, if appropriate, control of the differential pressures in the reverse osmosis modules by detection and, if appropriate, regulation of the hydrostatic pressures in the permeate water spaces, and optionally, the permeate water spaces are supplied with gases, gas mixtures or air and optionally hygenizing materials via aeration lines.The vessel system is referred to below as the entirety of modules which are fluidically connected to one another and of the connecting elements, i.e. suitable hoses or pipes including couplings which can optionally be sealingly closed on both sides, by means of which the fluidic connections described below are formed.A quantity of water is generally referred to as a body of water, wherein the boundary surfaces of the body of water are imaginary in the sense of the invention, since the method according to the invention is preferably carried out directly in a marine body of water and a mixing of the process water to be discharged with the surrounding body of water is advantageous. However, it is likewise possible for the method according to the invention to be carried out in a real enclosed body of water, for example in a tank.In the prefiltration, the seawater is passed through filters and / or membranes in order to separate small, but also larger, organisms, particles, suspended substances or colloids, i.e. materials which do not go into solution, from the water to be demineralized. The necessary degree of prefiltration with which such materials must be filtered out depends on the properties of the osmotic membrane filters and is specified for these by the manufacturer. Such prefiltration methods for osmosis and reverse osmosis and filter devices suitable for this are known to the person skilled in the art, so that it can select suitable methods and devices with knowledge of the properties of the osmosis membrane filter. Depending on the method chosen, the water to be demineralized can be prefiltrationed at various points before the exposure of the osmotic membrane filter to the water. For example, the pretreatment takes place close / at the surface of the body of water in a prefiltration module and thus enables simple cleaning and maintenance of the filters. Likewise, the prefiltration can take place in the fluidic connection to the reverse osmosis module, in the case of a plurality of modules at least first in their series arrangement, or else only in the process water space, provided this takes place in such a way that the osmosis membrane filter is only acted upon by prefiltrated water, i.e. by process water.The designations h i with (i=1,2,3,... ) and h a with (a= I,II,III.. indicate the depth of the "i"-th reverse osmosis module or of the "a"-th outlet distributor in the body of water. All depth elevations are equal to the perpendicular positive distance of the respective module from the surface of the water body. The water surface itself is assigned the reference height h 0=0. The hydrostatic process water pressure in the respective reverse osmosis module is correspondingly referred to as pressure p i. From this minus the salt content-dependent osmotic pressure, the pressure effective on the process water side for reverse osmosis is derived.The process water present in the reverse osmosis module leaves the latter either through the outlet arranged in the process water space or, after passing through the osmosis membrane filters, through a permeate water outlet arranged in the permeate water space.A process water stream is advantageously formed from the inlet of the process water space to the outlet of the process water space, wherein the process water stream in the reverse osmosis module has a hydrostatic process water pressure p i which is built up through the process water-filled vessel region to the depth h i of the reverse osmosis module. The depth h i defines the perpendicular positive distance of the drain of the i-th reverse osmosis module from the surface of the body of water, in other words the perpendicular distance measured from the surface of the body of water to the upper edge of the reverse osmosis module plus the perpendicular of the overall height of the, for example floating reverse osmosis module arranged in the body of water.The difference of process water pressure p i to the pressure in the permeate water space is set such that it is greater than the osmotic pressure resulting from the difference of the different osmotic potentials of process water and permeate water. As a result, at least a portion of the process water is forced through the osmotic membrane filters along the pressure differential. For this purpose, for the hydrostatic process water pressure p i determined by the immersion depth h i of the reverse osmosis module, a lower pressure in the permeate water space is set in such a way that the pressure difference to the process water pressure enables an efficient flow through the osmotic membrane filters, but does not destroy the latter or wear it prematurely. For this purpose, the permeate water space can be aerated via an aeration line, while the permeate water obtained is pumped out of the permeate water space by means of a pressurized water pump arranged in the permeate water space. If less or more permeate water is pumped off than is simultaneously fed via the osmosis membrane filters, the permeate water space and the aeration tube will fill until a respective equilibrium has been established between fed-on and pumped-off permeate water. The pressure in the permeate water space increases in proportion to the fill level in the ventilation tube and thus lowers the differential pressure to the process water space which determines the water flow. If the differential pressure drops to the salt content-dependent osmotic potential of the process water, no further permeate water is formed.The above-described functional mechanism is not linked to the ventability of the permeate water space and thus to a venting device. The aeration device enables the specification of a pressure which would be established in the permeate water space at a minimum if the permeate water obtained is completely removed. If no venting device is present or if it is closed, this pressure minimum is theoretically limited by the vapor pressure of the water under operating conditions.While the pressure minimum in the permeate water space optionally filled with air, gas or water vapor defines the state which enables the maximum permeate water stream under given operating conditions, the setting of the hydrostatic pressure p i minus the effective pressure in the permeate water space now filled, for example, with permeate water determines the state in which the permeate water stream disappears. Between these two states there is an "inner control range" for controlling the permeate water flow.Analogously, a hydrostatic pressure in the reverse osmosis module, which is equal in magnitude to the osmotic pressure, can use the minimum hydrostatic pressure required when it is exceeded, a filtration flow through the respective osmotic membrane filter, while the maximum possible hydrostatic pressure is defined by the load capacity of components of the plant, the thickness of the body of water and practical considerations for the operation of the plant. Between these two states is the "outer control range" for the permeate water stream, within which the depth of the reverse osmosis module in the body of water is (dynamically) adjusted.In order to realize the desired filtration flow of the process water through the osmotic membrane filters, the at least one reverse osmosis module according to an exemplary embodiment is arranged at a depth h i of more than 200 m below the water level.The system is adjusted, for example, for a closed permeate water space initially filled with water. When the reverse osmosis module is lowered or raised within the water column, the hydrostatic pressure in the process water space changes, which drives the flow of water via the osmotic membrane filters and leads to the hydrostatic pressure being established minus the osmotic pressure in the permeate water space, which pressure is determined by the different salt content between process water and permeate water. The pressurized water pump can now be switched on. The delivery rate thereof is increased until the pressure in the permeate water space (for example visible via the water level in the ventilation tube or a pressure sensor) signals a sufficient differential pressure with respect to the pressure in the process water space or until the currently desired delivery rate is reached.The reverse osmosis module is positioned in the body of water in such a way that the inlets and outlets of the module are suitably oriented in the body of water depending on its technical design. For example, all fluidic connections, i.e. inlets and outlets, could be located on the lower edge or upper edge of the module, whereby the module would be positioned above or below the connections in the body of water or the inlet of the process water chamber, for example, is positioned higher in the body of water than the outlet of the reverse osmosis module. In the case of a buoyancy-based positioning, the position of a gas reservoir acting as a buoyancy body, which is located in the reverse osmosis module or is mechanically connected to the latter, can be defined for this purpose in such a way that the common center of gravity of the arrangement of buoyancy body and reverse osmosis module defines the orientation of the reverse osmosis module in the body of water.In the reverse osmosis module, concentrated process water, i.e. process water with a higher salt concentration than that of the surrounding seawater, is accelerated by its increased density with respect to seawater in the direction of the lower outlet distributor and is thus moved from the inlet of the process water space of the reverse osmosis module in the direction of the outlet thereof.If a plurality of reverse osmosis modules are operated, these can be operated serially, i.e. in succession (also referred to as "in series") in the flow direction of the process water, each further reverse osmosis module being arranged at a depth h i, ( i=2, 3, 4... ) deviating from h 1. Alternatively or additionally, a plurality of reverse osmosis modules can be operated in parallel with one another and with separate / divided process water streams, wherein the reverse osmosis modules are arranged at the same depths h 1 or at different depths h 1 ≠ h i, ( i=2, 3, 4... ). Possibilities for the fluidic connection within the vessel systems are explained in more detail by way of example below with reference to the figures.The depths are designed or set in a plant- and operation-specific manner and, in the case of the serial arrangement, as a function of the separation performance, reverse osmosis modules through which process water has already flowed, if appropriate. The osmotic pressures of the process water to be compensated in the respective reverse osmosis modules enter the criterion for setting the hydrostatic pressures on the process water side as a minimum in terms of amount.The removal of water in the reverse osmosis modules leads to a stepwise concentration of salts in the process water on its way through the vessel system. The density p i( z) of the process water within the vascular system thus increases. The hydrostatic pressure at the discharge manifold thus reaches p i= p̅ i gh a, where g is the gravitational acceleration and p̅ i= h a-1 free following p i( z)dz is the average density that forms along z in the vasculature. The hydrostatic pressure in the body of water, which prevails at the depth of the outlet distributor h a is Pa= p̅gh a. Let p̅ = h a-1 following following following (z)dz be the density averaged over the depth h a and p(z) be the depth-dependent density distribution in the body of water. However, for p̅ i > p̅, each hydrostatic pressure difference Δp=p i- p a leads to a volume flow of process water exiting from the outlet distributor, whereby the reverse osmosis modules located above them are also supplied with further process water.In the stationary state, a flow through the vessel system is formed with a volume flow Q w whose size along the vessel system is determined by the separation performance of the reverse osmosis modules, the depth in the body of water, the depth of the outlet distributors and the hydraulic resistances in the vessel system and can be determined within wide limits by the design of the MWS system.Since the outlet distributor has the greatest perpendicular distance h a, i.e. the greatest depth of all the assemblies of the MWS system, the highest concentrated process water is located in the region between the upstream reverse osmosis module and the outlet distributor. This range can therefore decisively bring about a density-based acceleration of the process water flow through the vessel system, which is taken into account in particular in the design of the MWS plant.The density-based volume flow reduces the energy expenditure which is necessary or enables a completely passively operated provision of process water for the process water throughput in the entire device, for example with a sufficient depth of the outlet distributors.An initially possibly necessary energy expenditure for rapidly initiating the process water flow can thus be compensated, at least partially, in the course of the formation of a dense- or else gravity-driven flow through the vessel system. In particular, a system-specific design of the distance between outlet distributor and upstream reverse osmosis module thus makes it possible with comparatively little outlay (there is only a minimum of connecting elements here) to reduce to a minimum the energy outlay for generating the necessary process water throughput.The process water discharged from the outlet distributors is discharged, via an outlet nozzle which can be advantageously oriented, directed into the body of water, so that the recoil caused by the process water entering the body of water moves the outlet distributor in the body of water. This results in a large dilution volume. At the same time, the mixture with the water present there brings about an enrichment with oxygen, which can promote aerobic life and fish growth and can inhibit anaerobes (and any H 2 S formation coupled to their action).Permeate water can be obtained by dynamically regulating the depths of the individual modules as a function of, for example, their separation performance, the permeate water requirement or the optimum process water throughput (external control).In a further embodiment, the depths h i of the individual modules or module groups are controlled from the processing platform via cables (external control). In this embodiment, neither ventilation lines nor buoyancy bodies are necessary. The pressure water pumps are controlled by pressure measurements in the permeate water spaces of the reverse osmosis modules (control in the inner control range).In a further embodiment, such a depth regulation can be effected at least partially lift-based by proportional filling of the float bodies with gas or gas mixtures or water. Air is particularly suitable as the gas mixture, permeate water is particularly suitable as the water, or others are suitable as the water. In this embodiment, the buoyancy body can be connected fluidically to the ventilation line of the permeate water space. If the buoyant body is located outside the reverse osmosis module, then it would be coupled into the ventilation line, for example, close to the upper boundary thereof. The deeper the reverse osmosis module is to be positioned within the body of water, the more gas in the buoyancy body has to be replaced by water. In this embodiment, the pressurized water pumps convey permeate water which arises in such an amount that the gas fill level and, if appropriate, its pressure in the float can be controlled via the latter (outer control on the permeate water side).In a further embodiment, with the depth of the reverse osmosis modules remaining the same, the differential pressures and thus the permeate water streams are regulated by modulating the delivery rate of the pumps (internal regulation). As described above, the differential pressures with respect to the respective permeate water pressure in the reverse osmosis module will be set, for example, in accordance with the respective height difference between the water levels in the aeration pipes and the surface of the water and would be variable within wide limits by modulation of the delivery rate of the pumps (internal control). In this embodiment, the float can be provided with valves in order to close it after it has been filled in a defined manner (external control). Alternatively, the depth of the reverse osmosis modules in the body of water is controlled and fixed mechanically via cables from the processing platform. A buoyancy body is then not necessary.The possibilities listed for controlling the plant and thus the different possibilities for the external and internal control for adjusting the permeate water flow can be combined according to the invention and thus enable a robust and efficient plant operation. The adjustment of the pressure conditions desired for efficient filtration in the reverse osmosis modules is carried out as described above by the external and internal control specifically for each reverse osmosis module. On the basis of the concept, the MWS plant according to the invention operates more efficiently in terms of energy than the plants currently used in practice, which is to be shown by the following description:Assume that, on the permeate water side of a reverse osmosis module, the positive or negative pressure p p, is set with respect to the air pressure (here, p p=0) is used. Then, the pressurized water pump connected in or to the permeate water chamber has to apply at most the pressure p r= p H20 ghi-p p for lifting the permeate water up to the surface of the water. The work required for raising the water volume V is Pr V=P i- p p) V, which results in a pump output P=(P i-p p) Q to be applied for the volume flow Q=dV / dt. The efficiency is neglected here. If this pump output is compared for approximately the same pressure conditions with a plant corresponding to the prior art, in which the pump delivers the process water stream, this must deliver the output P i= p i Q W with a maximum of the separation degree of 0.5 described at the beginning being achieved. This means that the pump must convey a volume flow of approximately 2 Q w of process water in this case in order to generate the volume flow Q of permeate water. Based on the output of the pressurized water pump of the MWS system according to the invention, the delivery of this process water stream thus requires twice the energy output Q w / Q·P=2 P=P i. to be expended. This applies correspondingly to the work to be expended. In this estimation, it was assumed that the effort for the prefiltration is the same in both types of plants, the plant according to the invention was assumed conservatively on the permeate-water side to be air pressure in the permeate-water space, and the additional performance for the throttle valves necessary in conventional plants and, if appropriate, further pumps which move the permeate-water stream was neglected.The described method according to the invention thus has the effect, on the one hand, that the hydrostatic pressure p i itself drives the reverse osmosis as a function of the back pressure on the permeate water side via the pressure difference p i- p p. Therefore, no further energy needs to be expended for this purpose and a control of p i( external control) and / or p p( internal control) allows permanent setting of optimum operating conditions. On the other hand, the method has the effect that the energy expenditure depends only on the lifting of the actually filtered water quantity to the water surface, whereby the required delivery capacity of the pumps can be significantly reduced in relation to the prior art.The dense-driven flow through the vessel system which develops during the flow through the plant according to the invention reduces the energy and plant-related outlay for generating the necessary process water throughput to a minimum.The pumps, valves and further technical components required for the operation of reverse osmosis are now exposed for the most part only to demineralized permeate water in the MWS plant according to the invention and therefore operate under very largely low-corrosive conditions, compared to the process water, which increases the operating time of these assemblies. In addition, there are no particles and biological substances in the permeate water space which optionally reduce the service life of pumps, valves, sensors and further components.Substances which would be dissolved as a result of corrosion on the process water side are only still obtained within the plant according to the invention in a significantly reduced amount, based on the prior art, whereby the introduction of potential pollutants into the body of water is reduced.The construction according to the invention further allows different auxiliary substances, gases and / or chemical substances to be added in metered amounts on the permeate space side and optionally distributed on the membrane surface. Since osmotic membranes can be permeated in a permeable or diffusive manner for different substances and the driving force required for permeation follows from the difference of the substance-specific chemical potentials (e.g. concentration differences), this provides possibilities for supplying the osmotic membranes with these substances during operation both on the permeate water side and on the process water side without appreciably influencing the process water. This can be used to protect the osmotic membrane filters from precipitates, biofilms or other changes in the membranes or membrane surfaces, which can reduce the permeability or lifetime of the osmotic membrane filters.If the permeate water space is exposed to nitrogen instead of oxygen-containing air, for example, or a vacuum / partial vacuum or the water vapor pressure is used in order to set the permeate water-side pressure, the separation of, for example, metal hydroxides on the osmosis membranes can optionally be reduced and thus their run time can be extended. The controlled metering of gases and / or substances for hygienizing the permeate water obtained is also possible in this way in a simple and efficient manner. Since all the process water does not have to be enriched with these chemicals, this procedure would allow the use of such auxiliary substances to be limited to a minimum.Furthermore, during operation, it is possible to flush back the osmotic membrane filters by reversing the pressure conditions, in order to thereby detach floccules and documents from the process water-side surfaces of the osmotic membrane filters and flush them out of the osmotic membrane filters. For this purpose, for example, the pressurized water pump in the permeate water space would be closed by means of a valve and the permeate water collected there would be pressed through the osmosis membrane filters on the process water side thereof by the action of compressed air or a pressurized gas or gas mixture.For regeneration, maintenance or repair of the reverse osmosis modules, these are raised to the surface by means of ropes, via the pipe system or based on buoyancy, which is possible in particular in the case of modules operated in parallel without interrupting the production of permeate water by the remaining modules.To achieve the object according to the invention, a device is also specified, having:a first reverse osmosis module, which is fluidically connected to the upper end of a body of water and is arranged at a first depth h 1 in the body of water,wherein the reverse osmosis module comprises an outwardly encapsulated cavity with a process water space having an inlet and an outlet and a permeate water space which are separated from one another by osmotic membrane filters;at least one pump which is designed and configured to convey permeate water which arises in the permeate water space;at least one outlet distributor which is configured to be fluidically connected to the process water space of the reverse osmosis module by means of an outlet and is arranged within the water body at an outlet depth h a arranged below the first depth h 1 and which has an outlet directed towards the surrounding water; wherein the depth h 1 is configured such that a process water stream flows through the reverse osmosis module from the inlet to the outlet at a hydrostatic process water pressure p 1 present in the reverse osmosis module.The device can have the following features, wherein not all features are absolutely necessary: A floating processing platform positionable on the water surface with processing and control modules connected fluidically, electrically, in terms of control technology and mechanically to the modules listed below, components or modules for prefiltration of the water to be demineralized, which can be positioned in the inflow of the water to the osmomembran filter, for example in the body of the water, reverse osmosis modules and one or more outlet distributors which are connected fluidically by means of suitable pipe or hose lines via two separate water line systems and, if appropriate, a ventilation line and thus make possible a process water flow which moves from the surface of the body of water through the process water spaces of the reverse osmosis modules floating deeper in the body of water to outlet distributors arranged deeper in the body of water, and pressurized water pumps which convey the permeate water collected in the permeate water spaces of the reverse osmosis modules as permeate water streams to the processing modules on the processing platform, and also an (optional) aeration stream which, starting from the processing and control modules on the processing platform, feeds the permeate water spaces of the respective reverse osmosis modules and, if appropriate, buoyancy bodies arranged above or within the latter with gases, for example air, wherein the permeate water spaces within the reverse osmosis modules are equipped with: pressure sensors, a pressure water pump located in a sump and optionally valves for closing the permeate water lines connected to the permeate water spaces and / or the ventilation lines connected to the latter and through osmotic membrane filters are separated from the process water spaces which have an inlet and an outlet for the process water and are flowed through by the latter, wherein this vessel system, formed from the different modules and lines, can be positioned below, for example close to, the processing platform by ropes lowered from the processing platform and / or based on buoyancy in the body of water, andIn some embodiments, the outlet distributors have outlet nozzles which can be adjusted in their orientation and optionally regulated in order to distribute the process water over a large area in the surrounding body of water and in this respect benefit from the recoil which arises as a result of the introduction of the process water into the body of water.According to a further embodiment, the device has a processing platform floating on the surface of the body of water with processing and control modules located thereon. A processing and control module serves to accommodate elements which are necessary for mechanical, electrical, control and fluidic coupling with the prefiltration modules, the reverse osmosis modules, buoyancy bodies and outlet distributors, as well as for operation of the plant. Here, permeate water is taken up, its intended refining and the discharge, onward and / or transfer of the processed permeate water to the consumer, the plant control is carried out, for example with regard to the depth regulation of the reverse osmosis modules, the pressure and delivery quantity control, optionally the regulation of the process water discharged by the prefiltration modules or prefiltration devices, the orientation of the outlet nozzles, the metering of optionally necessary gases and substances via the ventilation line, etc. The permeate water reaching the processing module is refined (hygenized, enriched with missing mineral substances, etc.) there depending on the use, and then brought to land, for example via a pipe which is buoyant or laid in the body of water, optionally floating, or by ship.If a part of the processing platform is designed as a water reservoir, the density difference to the surrounding seawater leads to buoyancy, which can be used advantageously in terms of design, if appropriate. To provide the necessary electrical energy, the processing platform can optionally have an integrated power supply corresponding to the different technical possibilities.According to a further embodiment, the device has at least one prefiltration module arranged near the surface of the body of water and / or at least one prefiltration device, which has at least one filter surface and / or membrane surface and is designed to receive, prefiltrate and feed seawater as process water into a process water line or a plurality of process water lines. The prefiltration module can be configured to float on the water surface or be integrated into a floating or buoyant processing module, for example the processing platform, or it can be located on or below the water surface and be connected to the processing platform via a line system. The prefiltration module is encapsulated toward the seawater, whereby no uncontrolled water exchange occurs between an interior of the prefiltration module and the body of water surrounding it.In the prefiltration module and / or the prefiltration device, seawater is conditioned or pretreated to process water according to the plant-specific technical requirements of MWS plants by passing the seawater through suitable filters and / or membranes which are arranged in the prefiltration module and / or the prefiltration device. It is assumed that the pressure drop of the water to be filtered during the water movement through the prefiltration module and / or the prefiltration device can be neglected or remains small by using sufficiently large filter areas. Alternatively, pressure filtration can take place (optionally in a supporting manner) according to the prior art.If filters or membranes within a prefiltration module are mechanically connected, for example, to buoyant bodies floating on the surface of the water, then these can be moved in the filtration module as a function of the surface waves of the water because of the comparatively greater inertia of the prefiltration module, whereby filter surfaces can be cleaned, for example, and / or seawater can also be pressed through the filter device in a manner analogous to a membrane pump.The process water pretreated in the prefiltration module and / or in the prefiltration apparatus is supplied to the reverse osmosis modules via the inlets.According to the invention, at least one reverse osmosis module exists, which is configured to be fluidically connected via its inlet to a prefiltration module arranged upstream and / or to a prefiltration device and is arranged at a depth h 1 within the body of water. In this case, a location close to the outflow of the reverse osmosis module, for example close to its lower edge, is specified as a reference point for the respective depth specification. The definition of this reference point is motivated in that both the maximum acting hydrostatic process water pressure within the reverse osmosis module and the maximum hydrostatic head to be overcome are thus provided in order to convey the permeate water from an aerated permeate water space to the surface of the water.The reverse osmosis module comprises an outwardly encapsulated cavity with a process water space and a permeate water space. Both spaces are separated from each other by at least one osmotic membrane filter. The process water space has an inlet and an outlet, the permeate water space has at least one outlet, optionally also an inlet. In this permeate water space, a pressurized water pump including a pressure measuring device and a lockable nonreturn valve is preferably installed inside a sump, which pressurized water pump is designed and configured to convey the permeate water arising in the permeate water space via the permeate water line to the processing platform and in the process to regulate the pressure inside the permeate water space at a definable level.A "outwardly encapsulated" cavity is understood in the sense of the invention to mean that the outer wall of the cavity in the reverse osmosis module is formed from such an impermeable material and is manufactured in such a way that an exchange of seawater, process water, permeate water or gases through the wall is prevented. The outer wall of the reverse osmosis module can be formed in particular from plastics, metals or alloys or combinations thereof. It is thus possible without exception to supply media (process water, permeate water, gases, chemical substances) via the corresponding connections to the process or permeate water space of the reverse osmosis module.According to one embodiment, the reverse osmosis module for conveying the permeate water in its permeate water space has a low-lying sump, that is to say a region of the permeate water space which is situated lower than that part of the permeate water space in which the osmosis membrane filters are arranged and which is intended to accommodate a pressurized water pump for conveying the permeate water to the processing platform.If suitable radially filtering osmotic membrane filters are used, the permeate water space located within the reverse osmosis module is formed by its preferably cylindrical interior space plus the interior volume of the piping to further osmotic membrane filters and to the connections for the pressurized water pump and optionally the ventilation line and optionally the interior volume of a suitably arranged buoyancy body. In this preferred arrangement, the process water space therefore encloses the permeate water space on all sides.Osmotic membrane filters are made from semipermeable membranes which are permeable to water molecules, but at the same time are almost impermeable to salts and larger molecules, colloids or particles. In this way, only demineralized water, which is virtually free of dissolved or particulate constituents, passes into the permeate water space. Substances retained by the osmotic membrane filter must be permanently removed, which can preferably be effected with the continuous process water flow along the process water-side surface of the osmotic membrane filters.According to a further embodiment of the device, the reverse osmosis module is designed such that it can be positioned floatingly within the body of water due to its buoyancy. For floating positioning, the reverse osmosis module advantageously has a buoyant body which can be filled with gas and water and is located within the reverse osmosis module or mechanically coupled thereto, preferably floats above the reverse osmosis module in the body of water. By regulating the gas / water content in this buoyancy body, the buoyancy and thus the depth of the reverse osmosis module within the water body can be varied and thus the hydrostatic pressure of the process water in its process water space.As an alternative to a separate buoyancy body, the outer shell of the reverse osmosis module can also be designed in such a way that it gives the reverse osmosis module the desired buoyancy, which enables floating positioning within the body of water. In particular, this can be done by a double wall and / or a suitable selection of material, which is within the scope of the skilled person.According to the invention, there is at least one outlet distributor which is designed to be fluidically connected to the process water space of the upstream reverse osmosis module via its outlet and is arranged at an outlet depth h a within the water body and which has an outlet directed towards the surrounding water.The outlet distributor is preferably fastened to a hose or a flexible tube and can thus move within the body of the water, for example similar to a pendulum. The discharge of process water via the outlet distributor into the body of water leads to a force directed against the outlet distributor. The outlet distributor is thereby subject to a recoil. This provides the possibility for its movement within the body of water, optionally by varying the outflow direction via an orientable outlet nozzle. The process water can thereby be mixed into the body of water over a wide range and thus diluted over a large area.Therefore, the outlet of the outlet distributor has at least one outlet nozzle via which the process water is discharged from the outlet distributor directed into the surrounding water. The orientation of the outlet nozzle is preferably variable. The variation of the orientation of the outlet nozzle can take place either passively (randomly), i.e. for example due to the forces acting on the outlet nozzle associated with the flow in the vicinity of the outlet nozzle, or actively, i.e. by a controlled orientation of the outlet nozzle, for example.The pipe and / or hose system, which serves for supplying the reverse osmosis modules and outlet distributors with process water, is scarcely exposed to differential pressures across the wall thereof, since water of similar density is present both on the inside and on the outside of the pipe and / or hose system. This enables its flexible, i.e. non-rigid, design and thus enables within certain limits free mobility of the reverse osmosis modules and thus also their independent buoyancy-based depth regulation. Flexibility can also be realized, for example, via movable articulated shafts within an otherwise rigid pipe system. Correspondingly, also for the permeate water lines to the surface of the water, only small differential pressures apply across the wall thereof. Only the ventilation lines, which may be provided, are intended to withstand a high differential pressure across the wall, but may have a cross section smaller by a factor of 100 to 1000 than the permeate water lines, as a result of which the comparatively high curvature of their wall has a stabilizing effect against the external pressure. Thus, relatively flexible materials can also be used for these lines, which are optionally provided with supporting spiral inserts. All supply and conveying lines can be combined, for example, in the form of bundles and are connected to the respective module connections of the vascular system by couplings which can be closed in a watertight manner, if appropriate.According to a further embodiment, at least one of the fluid connections between, if appropriate, a prefiltration module, a first reverse osmosis module, if appropriate further reverse osmosis modules and outlet distributors is formed by means of flexible tubes and / or hoses.To carry out the method according to the invention, a reverse osmosis module is already sufficient that is positioned 1 in the body of water at a depth h. As explained above, however, a plurality of reverse osmosis modules can also be coupled to one another, for example in order to achieve the desired degree of concentration of salts in the process water, in order to be able to provide the desired amount of demineralized water or in order to optimize the efficiency of the process.According to a further embodiment, at least one further reverse osmosis module is arranged in the fluidic connection between the outlet of the process water chamber of the first reverse osmosis module and the outlet distributor at a depth h 2 deviating from the depth h 1. The outlet of the respective upper reverse osmosis module is fluidically connected via flexible tubes and / or hoses to the inlet of the underlying reverse osmosis module, so that process water from the first reverse osmosis module is transferred into the process water space of the following reverse osmosis module and there partially passes through the osmosis membrane filters located therein. Such an arrangement of a plurality of reverse osmosis modules is referred to below as a series circuit. By connecting a plurality of reverse osmosis modules in series, the salts in the process water are concentrated stepwise.In such an embodiment, the depth of the first reverse osmosis module h 1 and the further reverse osmosis modules h 2, h 3... h i located within the row are adjusted in such a way that the process water stream flowing through these modules in each case has hydrostatic process water pressures p 1< p 2< p i< p i+1... therein, which, taking into account the concentration of the process water, sufficiently exceed the osmotic pressure thus growing and thus achieve a sufficiently high permeate water stream. The specific depths depend here on the development of the osmotic pressure in the vascular system and thus on the technical design of the osmotic membrane filters in the respective reverse osmosis modules.The cross sections of the outlets and / or inlets of a plurality of reverse osmosis modules arranged in series may deviate from one another. For example, these may become smaller with increasing depth h i in the body of water and thus be designed for process water lines of smaller cross section. The latter would allow, for example, a uniform flow rate of the process water stream in the vessel system to be maintained despite the reduction in the mass flow of process water resulting from the acquisition of permeate water.In a further embodiment of the invention, one or more further reverse osmosis modules can be arranged in the fluidic connection between the prefiltration module / s and the outlet distributor / s at depths h i deviating from the depth h 1 of the first reverse osmosis module or approximately at the depth h 1 in the body of water. Such an arrangement of a plurality of desalting strings is referred to below as a parallel arrangement of reverse osmosis modules.An MWS plant configured in this way comprises a plurality of desalting strings operable in parallel. The reverse osmosis modules of the different strands can be designed in the same way or differently from one another. The feed of each strand can be supplied with process water from a separate filtration module or the strands use a common feed which is fed from a common filtration module. The desalting strings may be fed to a common outlet to a common outlet distributor or may have individual outlets to separate outlet distributors.The above statements on serial arrangement are analogously applicable to the individual desalting strings of the parallel arrangement. In particular, further reverse osmosis modules can in turn be linked to one another in series within the parallel strands.Different reverse osmosis modules can be combined structurally for both the serial and parallel arrangements. For example, the modules may contain different numbers of osmotic membrane filters.The invention is explained in more detail below with reference to exemplary embodiments and associated drawings. Figure shows FIG. 1 : shows a schematic illustration of a reverse osmosis module of a device according to the invention; FIG. 2 : shows an embodiment of the device according to the invention with a plurality of reverse osmosis modules connected in series; FIG. 3 : shows a further embodiment of the device according to the invention with a plurality of reverse osmosis modules connected in series; FIG. 4 : shows an embodiment of the device according to the invention with a plurality of reverse osmosis modules connected in parallel; and FIG. 5 shows a further embodiment of the device according to the invention with a plurality of reverse osmosis modules connected in parallel.The drawings show the apparatus only schematically to the extent required to explain the invention. They do not claim completeness or scale. The person skilled in the art would combine the features of the invention disclosed here with one another in further exemplary embodiments, provided that this appears expedient and possible.FIG. 1 shows a schematic illustration of a reverse osmosis module 1 of a device according to the invention.The reverse osmosis module 1 has an encapsulated cavity with a process water space 4 and a permeate water space 5. Optionally, the permeate water space 5 can have an access (not shown) which can be sealed in a gas-tight manner and which can serve for ventilating the permeate water space 5.The process sequence can be summarized as follows: process water flows through an inlet 2 into the process water space 4, wherein the process water flow, including permeation, is indicated in FIG. 1 by arrows in phantom. The hydrostatic process water pressure p 1 prevailing in the reverse osmosis module 1 enables a portion of the process water to pass through the osmosis membrane filters 6 arranged between the process water space 4 and the permeate water space 5 and to flow into the permeate water space 5 which is at a lower pressure. Components 11 of the process water which cannot permeate through the osmotic membrane 6, such as dissolved salts, are retained in the process water chamber 4 by the osmotic membrane filters 6. Demineralized water, which is referred to as permeate water, passes into the permeate water space 5.Concentrated process water remains in the process water space 4, which flows off through an outlet 3 arranged in the lower region of the reverse osmosis module.In the lower region of the permeate water space 5 there is a sump 12, that is to say a region which is lowered in comparison with the rest of the permeate water space 5 and in which there is arranged a permeate water outlet 8 and a pump 13 connected thereto for transporting away the permeate water.FIGS. 2 to 5 show different embodiments of the device according to the invention, each arranged within the body of the water of a marine body of water, i.e. of a sea or ocean, from which demineralized water is to be obtained.Common to all the illustrated embodiments is a processing platform 14 floating on the surface of the water, on which the control and processing modules of the MWS plant are erected.In the embodiment shown in FIG. 2, a pre-filtration module 9 is arranged directly on the processing platform 14, in which the seawater is preconditioned to process water by suitable filters and membranes.A first reverse osmosis module 1, which is located at a first depth h 1 in the body of water, i.e. below the water surface (reference height h o) is fluidically connected to the prefiltration module 9 via a suitable hose- or tubular fluid connection 10. The hydrostatic process water pressure p 1, which is built up by the depth h 1 of the reverse osmosis module 1 in the body of water, prevails in the interior of the first reverse osmosis module 1. The process water reaches the first reverse osmosis module 1 via the inlet 2 from the fluid connection 10 and leaves the latter via its outlet 3.The concentrated process water, which leaves the process water space of the first reverse osmosis module 1 via the outlet, reaches a further reverse osmosis module 1.1 situated at a lower level via a further fluid connection. This is located at a second depth h 2 below the water surface and has in its interior a hydrostatic process water pressure p 2 which is higher than p 1. In the second reverse osmosis module 1.1, a further concentration of the process water takes place, which in turn leaves the second reverse osmosis module 1.1 via an outlet and reaches a third, lower reverse osmosis module 1.2 via a further fluid connection. This is located at a third depth h 3 below the water surface and has in its interior a hydrostatic process water pressure p 3 which is higher than p 2.The further concentrated process water leaves the third reverse osmosis module 1.2 via an outlet distributor 7 which is fluidically connected to the outlet of the third reverse osmosis module 1.2 and via which it is finally discharged into the surrounding water. The outlet distributor is located at an outlet depth h a.For the construction of the reverse osmosis modules, reference is made to FIG. 1 and the description thereof. Alternative functionally comparable embodiments are possible. Accordingly, the three reverse osmosis modules 1, 1.1, 1.2 each have, in their respective permeate water space (corresponding to the illustration in FIG. 1 ), a pump 13 for transporting away the permeate water to the water surface (reference height h 0), preferably to the processing platform 14. The fluid connections of the respective permeate water spaces to the processing module are advantageously likewise flexible and are not illustrated in FIGS. 2 to 5.The embodiment shown in FIG. 3 differs from the embodiment shown in FIG. 2 only in that the prefiltration module 9 is not arranged directly on the processing platform 14, but is connected to the latter via a fluid connection 10. The prefiltration module 9 is also designed in such a way that it floats on the water surface.The depth difference between h 3 and h a both in FIGS. 2 and 3 is only schematically shown. As described above, it is preferred that this is significantly larger, for example at least as large as the depth differences between the individual reverse osmosis modules 1, 1.1, 1.2 or larger.FIGS. 4 and 5 each show an embodiment of the device according to the invention with a plurality of reverse osmosis modules 1.1 connected in parallel.In both embodiments, the prefiltration modules 9 are arranged directly on the processing platform 14. Alternatively, a flexible fluid connection of the prefiltration modules 9 to the processing platform 14 is also possible here.In the embodiment shown in FIG. 4, three reverse osmosis modules 1.1 are arranged in parallel at a depth h 1 below the water surface. The process water pressure p 1, which is built up by the depth h 1 of the reverse osmosis modules 1.1 in the body of water, prevails in the interior of all three reverse osmosis modules 1.1. The concentrated process water leaves the apparatus via an outflow distributor 7, which is arranged at the outflow depth h a.FIG. 5 shows an exemplary embodiment in which three reverse osmosis modules 1, 1.1, 1.2 are connected in parallel and are each fluidically connected to a separate prefiltration module 9. A first reverse osmosis module 1 and a further reverse osmosis module 1.1 are arranged at a first depth h 1 below the water surface. A further reverse osmosis module 1.2 is arranged at a second depth h 2.All three reverse osmosis modules 1, 1.1, 1.2 are each fluidically connected to a separate outlet distributor 7. The outlet distributors are arranged at different outlet depths h I, h II, h III in this case.List of reference characters1 Reverse osmosis module 2 Feed 3 Outlet 4 Process water space 5 Permeate water space 6 Osmotic membrane filter 7 Outlet distributor 8 Permeate water outlet 9 Prefiltration module 10 Fluidic connection 11 Filtered constituents 12 Sump 13 Pump 14 Processing module h 0 Sea level height (equal to reference height) h i Depth of the respective reverse osmosis module in the body of water h a Depth of the outlet distributor in the body of water P i Process water pressure

Claims

Method for obtaining demineralized water, called permeate water, from a marine body of water, comprising the steps of - providing at least one reverse osmosis module (1) which is fluidically connected to the upper end of the marine body of water at a depth h i, where i is an element of the natural numbers and i>0, within the body of water, wherein the reverse osmosis module (1) comprises an outwardly encapsulated cavity with a process water space (4) having an inlet (2) and an outlet (3) and a permeate water space (5) which are separated from one another by at least one osmosis membrane filter (6); and - providing an outlet distributor (7) which is fluidically connected to the outlet (3) of the process water space (4) of the reverse osmosis module (1) at an outlet depth h a within the body of water, wherein the outlet distributor (7) has an outlet directed towards the surrounding water; - prefiltration of a part of the body of water which flows towards the process water space (4) before its contact with the osmosis membrane filter (6) in order to form process water; - positioning of the reverse osmosis module (1) in the body of water at a depth h i in such a way that a part of the body of water flows through the inlet (2) of the process water space (4) towards its outlet (3), in order to form a process water stream in the process water space (4); forming a hydrostatic process water pressure p i in the process water space (4) of the reverse osmosis module (1) by adjusting a depth h i of the at least one reverse osmosis module (1) in the body of water in such a way that a pressure gradient is formed from the process water space (4) to the permeate water space (5) and consequently at least a part of the process water is pressed through the osmosis membrane filter (6) along the pressure gradient; and draining permeate water from the permeate water space (5).Method according to claim 1, wherein the depth h i of the at least one reverse osmosis module (1) and thus its hydrostatic process water pressure p i in the process water space (4) is set within such a pressure range which is limited by the minimum possible hydrostatic process water pressure p i, which is required for generating permeate water, and a maximum value of the hydrostatic process water pressure p i, up to which the components of the plant are protected from overloading thereof.Method according to one of claims 1 or 2, wherein the process water is provided by a pretreatment, in particular a prefiltration, of seawater.Method according to one of Claims 1 to 3, wherein the flow speed of the process water through the process water space (4) is set by means of the difference depth between the depth h i and the outflow depth h a of the at least one reverse osmosis module (1) in the body of water, wherein h i< h a.Method according to one of claims 1 to 4, wherein the depth h i of the at least one reverse osmosis module (1) is regulated by a change in the buoyancy force of the reverse osmosis module (1).Method according to one of claims 1 to 5, wherein the pressure difference between process water space (5) and permeate water space (4) and the permeate water inflow dependent thereon is regulated by means of the pressure in the permeate water space (5) by varying the permeate water outflow.Method according to claim 6, wherein the permeate water inflow is regulated by exposing the permeate water space (5) to air or a gas or a gas mixture via a fluidic connection and maintaining or varying air, gas or gas mixture at a predefined overpressure or underpressure p p, with respect to the air pressure while maintaining a pressure gradient from the process water space (4) to the permeate water space (5).The process according to any of claims 1 to 7, wherein at least one auxiliary substance is added in metered amounts on the permeate space side.Device for carrying out the method according to one of Claims 1 to 8, having: - a reverse osmosis module (1) which comprises an outwardly encapsulated cavity having a process water space (4) which has an inlet (2) and an outlet (3) and a permeate water space (5) which are separated from one another by at least one osmosis membrane filter (6); - at least one outlet distributor (7) which is fluidically connected to the outlet of the process water space (4) in order to be arranged below the reverse osmosis module (1) at an outlet depth h a and has an outlet directed towards the surrounding body of water; at least one prefiltration module (9) and / or a prefiltration device, having filters and / or membranes and designed for separating organisms, particles, suspended particles or colloids from the water to be desalted before its contact with the osmosis membrane filter (6), for forming process water; wherein the reverse osmosis module (1) is designed to be positioned within a marine water body and operated with process water; positioning means, designed on the reverse osmosis module (1) for its positioning at a variable depth within a marine water body; wherein the cavity of the reverse osmosis module (1), its inlet and outlet and the outlet distributor (7) are designed such that a process water stream flows through the process water space (4) solely on the basis of the gravity of the process water and a hydrostatic pressure can be built up in the cavity, formed by the height of the process water present above the reverse osmosis module (1) taking into account the average density thereof; at least one pump (13) which is designed and configured to convey permeate water which is produced in the permeate water space (5) such that the pressure thereof in the permeate water space (5) is maintained at a definable or variable level.Device according to claim 9, wherein the positioning means are configured to position the reverse osmosis module (1) at a depth h 1 in the body of water to form a hydrostatic process water pressure p 1 in the process water space (4).Device according to claim 9 or 10, wherein at least one further reverse osmosis module (1.1, 1.2) is arranged in the fluidic connection between the upper end of the water body and the outlet distributor (7) at a depth h 2 deviating from the depth h 1 or at the depth h 1.Device according to claim 9 or 10, wherein at least one further reverse osmosis module (1.1, 1.2) is arranged in the fluidic connection between the outlet (3) of the process water space (4) of the first reverse osmosis module (1) and the outlet distributor (7) at a depth h 2 deviating from the depth h 1.Device according to claim 11 or 12, wherein at least one further outlet distributor (7.1, 7.2) is fluidically connected to at least one further reverse osmosis module (1.1, 1.2) via its outlet (3).Device according to one of Claims 9 to 13, wherein a reverse osmosis module (1) is designed in such a way that it can be positioned in a floating manner within the body of water on account of its buoyancy.Device according to one of Claims 9 to 14, wherein the outlet of the outlet distributor (7) has at least one outlet nozzle which is aligned decentrally with respect to a central axis of the fluid access of the outlet distributor (7) and / or the alignment of which is variable.

Images