WO2015198080A1

WO2015198080A1 - Using high frequency vibration for operational improvement of membrane filtration process

Info

Publication number: WO2015198080A1
Application number: PCT/GR2015/000032
Authority: WO
Inventors: Konstantinos Chatzikonstantinou
Original assignee: Konstantinos Chatzikonstantinou
Priority date: 2014-06-27
Filing date: 2015-06-29
Publication date: 2015-12-30
Also published as: GR1008540B

Abstract

The present invention provides method and system for controlling membrane fouling in a membrane filtration process which is well tested in a pilot MBR system treating synthetic wastewater (SWW) as a municipal simulated wastewater, using small copies of commercialized modules and different type of membranes working for a long period, wherein said fouling control includes high frequency membrane vibration. The mechanical energy of vibrated apparatus is used to create and/or increase the shear-rate at the interface of the membrane filtration element in order to increase or improve rejection of the remaining or stacked elements, thus reducing or eliminating the accumulation of these retentate compounds, which causes blockage of the membranes. The method and system according to the present invention, works in situ at the relaxing intervals of the filtration process in a continuous or intermittent mode. The results of the present invention in accordance with the attached diagrams proven that there is no need of continuous use of HFPV process, as if a periodic vibration applied. The main goal of this invention was to establish a method/system to prevent or to remove deposits from filtration membranes used in a fluid separation process, by means of vibrators coupled either directly to the membranes or to the frame bearing said membranes, wherein the vibration applied in periods of membranes relaxing, which alternate with periods of active filtration, without vibration. Vibration can take place mainly in a direction parallel or perpendicular to the surface of the membranes themselves or the surface of the array of membrane elements, at amplitude ranging from 0.1-1.5 mm, but also in other directions, at smaller amplitude. Preferably vibrator's frequency ranges from 20 to 600 Hz, wherein the frequency, amplitude and/or waveform of the vibration can be constant or may be varied, during the membrane cleaning process and can be properly regulated according to the system needs, with an advanced monitoring operational system. It is a further object of this invention to provide an MBR system that does not utilize membrane air scouring as main cleaning process but as an associated cleaning system and process thus reducing energy consumption. In addition one more issue of this invention is to provide a new approach for the membranes' cleaning, taking into consideration for the first time the cleaning water temperature in a tank or in backwash process with or without vibration.

Description

USING HIGH FREQUENCY VIBRATION FOR OPERATIONAL IMPROVEME T OF

MEMBRANE FILTRATION PROCESS DESCRIPTION

FIELD OF THE INVENTION

The present invention is related in general to the field of fluid separation using membranes, and more particularly, to fluid separation systems having hollow fiber membranes or flat sheet membranes, or a plate and frame membrane which is susceptible of backwards cleaning, or a combination of them, or a tubular module, or capillary module.

In particular the present invention relates to the operational improvement of the filtration process by fouling control in the membrane surface, by applying high frequency power vibration (HFPV). The application of vibration is made either in situ in the operating position of the device or externally, in a suitable receiving tank as a cleaning procedure. The application of the high frequency vibration may be combined with other associated cleaning systems and processes such as backwashing of the membrane or the application of liquid jet cleaning or gas air scouring.

BACKGROUND OF THE INVENTION

The membrane technology is successfully used as a separation technology in recent decades mainly in chemical processes and has already established itself as a valuable tool for filtering and cleaning of industrial process water, groundwater and surface water as well as wastewater.

The difference of membrane technology over other separation processes is the fact that it operates without the addition of chemicals with relatively low energy consumption, is relatively easy to operate, and can be flexible and easily expandable.

Progress in manufacturing technology of membranes over time makes most membranes increasingly competitive to conventional techniques.

The membrane separation process, based on the presence of semi-permeable membranes. The principle of operation is very simple: the membrane acts as a selective partition wall that allows the flow of fluid to pass from inside, holding the suspended solids and other substances such as proteins, viruses, bacteria etc. Some substances can pass through the membrane, while others are retained on the surface thereof.

During filtration, membrane fouling or clogging of solids is inevitable, even with adequate pretreatment. The type and degree of fouling depend on many different factors, such as type of treated fluid, type of membrane, the membrane materials design and process control.

Membrane fouling caused by the attachment of suspended solids and soluble substances on the membrane surface is the major barrier for the widespread application of MBR technology. The various types of pollution can be identified as follows (Judd, 2004; Liao et al., 2004): • Clogging is a progressive accumulation of dry sludge in module volume, starting from "dead zones" in the reactor.

• Sludging refers to an accumulation of sludge at surface of membrane.

• Fouling represents all mechanisms of cake building, plus adsorption/blockage into membrane material.

In MBR, the hydrodynamics are of great importance for reducing sludge deposition on the membrane surface and prolonging the operating period below the critical TMP.

Filter's manufacturers are continually searching for new materials that will improve the properties of the membranes and methods for improving the operation thereof, or intervening in the control of the process either in the design of devices/modules used. The aim is to reduce malfunctions and operational costs for prolonged periods even when processing fluids with high solids contents and/or colloidal materials, aiming simultaneously to reduce energy consumption.

So manufacturer's design includes a wide range of materials and configurations used in the effort to implement continuous filtration processes. This need has led to several known techniques to prevent accumulation of contaminants on the membrane surface, that might blocked it gradually, and does not allow the passage of liquid through the filter by reducing the flow (flux) and increasing the filtration pressure (TMP).

The most accepted methods for cleaning the membrane surfaces is the application of relatively high flow of air bubbles along the surface filtration, the relaxation of the membranes for short intervals, the backwashing and chemical cleaning. These techniques are used either continuously or intermittently, for the periodic cleaning of the surfaces of the filters.

However all these techniques and their variants are generally inefficient over a long time period and costly methods, including labor costs, and finally lead to shrinkage of the lifetime of membranes and ultimately to non-acceptance of successful membrane technology.

The method has been adopted by most manufacturers for fouling control is the application of air scouring with compressed air in the form of an upward bubbles flow (mostly coarse bubbles).

Membrane performance measured in terms of membrane fouling has been observed to be enhanced by gas sparging and reports have shown improvements up to 63% when air is introduced (Bellara et al., 1996; Berube et al., 2006; Cui et al., 1997).

It has been found that bubbling can limit surface fouling (clogging and sludging), but not internal fouling (adsorption and pore blockage).

A general observation for H.F. membranes is that larger airflow rates decrease the rate at which the pressure rises due to fouling, but that enhancement reaches a "plateau" as gas flow rate increases (Katsoufidou et al., 2005). This is also depended, according recent studies, to the tightness of hollow fiber, or diameter, or liquid viscosity etc (Wicaksana et al., 2005). Moreover it is difficult to ensure a homogenous bubble distribution (Genkin et al., 2006, Wu et al., 2008) and aeration at higher velocities can change sludge properties and hence diminish the biomass floe stability (Rosenberger and Kraume, 2003, Drews et al., 2005).

The peak of shear stresses induced by bubbling were up to 45% higher compared to when no bubbling was applied (Ducom et al., 2002).

The experimental challenge in submerged hollow fiber systems with bubbly flow is to characterize the shear stress domain. Also the shear stress is affected by the activated sludge composition and properties such as floe size and cake porosity (Wisniewski and Grasmick, 1998).

A lot of efforts have been exploited in the past in this direction of the combination of used purification techniques together with mechanical actions and techniques. Some of these have shown that by applying vibration to the membranes it is possible to improve the hydrodynamic limitations shown in membrane separation process.

Although all the referred studies reported a significant improvement on both the Critical Flux (CF) and the sustainability of operation, they face numerous limitations such as: (1 ) the vibrating system is often restricted to a small range of vibration amplitudes and frequencies; (2) because of the membrane element is separated from the vibration engine, without the use of anti- vibration devices, the obtained yield of shear rates is somehow reduced, due to energy loss resulting from the mechanical contacts and their friction; (3) in most cases, filtration running in a fixed vibration mode, without the ability of changing the vibration parameters during the filtration or cleaning process, therefore it is not able to adapt to application needs of the mixed liquor that might change over time; (4) in most studies the offered vibration power was limited; (5) in most studies experiments were performed in a very short time span of few minutes or hours in which it is not certain that there is a realistic simulation of clogging of membranes used in order to be able to draw conclusions; (6) in some cases detection limits of the used measuring devices were limited or measurements based on estimations (e.g. measurements that relate to the speed of the suction pump and not the actual flow); (7) in most cases, was not used real or simulated waste water as an influent; (8) few research was done to examine the impact in different material and type of membranes; (9) the examined systems and techniques are not feasible to be used in currently known SMBR modules, especially due to the large vibration amplitude. In all studies, experiments took place not during membrane relaxation period (all of the used "plastic" membranes need a small period of time for relaxation to recover their characteristics) but during filtration (10).

Considering the limited efficiency of the coarse bubbles aeration in submerged MBR's, the enhancement of shear rate via mechanical means seems a potential option for fouling control.

The enhancement of shear-rate at the feed side of the membrane is the most efficient way to control fouling. It increases the back-transport of retained compounds and reduces the concentration polarization and the cake build-up (Jaffrin, 2008). Shear-enhanced filtrations have been developed in several proposed filtration technologies. It includes rotating cylindrical membranes, rotating disk systems and vibrating systems (Jaffrin, 2008).

US Pat. Nos. 4,872,988; 4,952,317; 5,014,564; 5,985, 160; 5,725,767 and 6,322,698; 6,596, 164 and 6,872,301 apply relatively violent reciprocating, torsional vibrations of enclosing vessels, stacked filter leaves or plate frame filters along with associated plumbing and connecting devices, and the contained process fluid. Relatively high construction costs may be required to build structures that can withstand these constant reciprocating motions and high amounts of energy often required. Moreover, it requires a high complexity and safety level to operate those techniques. Therefore, those techniques have a low applicability, and are limited to certain specialized applications.

Another method used to inhibit membrane clogging by caking, scaling or filming, is the use of air bubbling technique. US. Pat. No. 6,287,467 reported a cleaning procedure in parallel mounted flat leaf elements via air bubbling. The associated leaf filter elements generally require maintenance of uniform, structurally braced spacing between each filter leaf element to provide access for air bubbles to all membrane surfaces. The rigidly held membrane surfaces may provide a highly stable platform on which solids cake may build up which the air bubbles can no longer remove such that manual cleaning may be required. Also due to relatively weak shear forces the increment of air flow cannot improve proportionally the flux an effective bubble distribution cannot be guaranteed.

Muhammed Roil Bilad and Ivo Vankelecom in their invention publication (WO 2012083390 A3) describe the use of a method and filtration system that applies magnetically induced vibration of membranes to provide shear enhancement on the membrane surface.

In this system, the vibration parameters (frequency and amplitude) can be adjusted, programmed or automatically controlled. The membrane moves based on electromagnetic attraction and repulsion in a 'push and pull' mode, in a direction parallel to the membrane surface. The referred study reported a significant improvement on both the Critical Flux (CF) and the resistance, although there were measured at very small intervals between 30 - 300 min of operation as the authors themselves mentioned.

They also found that the implementation of vibration generally controls the fouling by preventing, limiting, inhibiting and removing the foulant build-up, thus increasing membrane fluxes, reducing the down time of operation, reducing the cleaning frequency of the membranes and, consequently, enhancing membrane lifetime and overall decreasing costs of the filtration process, which is of particular importance in large scale and/or low cost application, such as^' waste water treatment.

This, together with less energy loss in mechanical friction, also lowers the energy consumption. These demonstrate the usefulness of the technique used, although in this invention is not considered important issues such as the size of the vibration energy losses and the real sizes of vibration applied to the membranes, temperature influence in the measured data, whilst no information is provided for the holding apparatus of the membrane elements during the phase of vibration.

Also according the authors (M. Bilad, et al., 201 1) it has to be noticed that this experiment was performed in a very short time span, so apart from the attachment of biofoulants, physico- chemical interactions were not observed due to short duration and the detection limits of the pressure gauges and also all experiments took place during filtration.

Moreover the small bioreactor working volume of 18.6 It which was "virtually" divided into aerated and non-aerated zones might strongly affect the measurements, such as measurements based on estimations (e.g. measurements that relate to the speed of the suction pump and not the actual flow and real vibration power of the vibration device calculated approximately from the electric current and electrostatic potential measured on the electrical wire).

Finally during the filtration experiments according to authors, all the measurements were done, with a vibration adjusted frequency between 0-60 Hz, and amplitude limited to 2mm, but it is not stated how those figures were measured and with what accuracy.

So according to the above-mentioned approaches the main drawback of known filters and especially MBR systems is membrane fouling and the successful way of treating it. The use of air scouring is not the optimal and ultimate answer to the problem, as it is energy intensive, produces a relative weak shear rates and it is difficult to ensure a homogenous bubble distribution on the surface of the membrane element (Genkin et al., 2006; Wu et al., 2008).

Thus, a need exists in reducing membrane fouling in filters improvement and especially in MBR systems, that reduce membrane fouling and that do not rely upon air scouring. The present invention is aimed at fulfilling these and other needs in the art. DETAILED DESCRIPTION

For a better understanding of the nature and advantages of the invention may be acquired by referring to the following description taken in conjunction with the accompanying figures/drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention relates to the field of fluid separation using membranes and especially to membrane bioreactors (MBR's). The various details of the present invention, are described in greater detail hereinafter. Preferred embodiments of the invention and its advantages are best understood by reference to Figs. 1 & 4.

The term "membrane" in this application means any material, particularly porous ή διάτρητο material, acting as a semi-permeable separation layer. The term "membrane" may be used in this application to mean any material having openings or pores satisfactory for use in separating a process fluid into a clarified fluid stream and a concentrated fluid stream.

The term "flat sheet membrane" is used to describe any membrane in flat form that is mostly attached to a support layer. Typically, the active separation layer is on the outer surface facing the filtered fluid.

The term "hollow fiber membrane" may be used to describe any membrane that generally forms hollow elongated tubes. Typically, the active separation layer is at the outer surface of the hollow tubes.

"Process fluid" may be generally defined as a fluid stream (liquids and/or gasses) containing liquid together with fouiants such as suspended solids, colloidal matter and/or particulate matter etc.

The clogging or fouling materials that may consist of particulates, solids, sludge cakes, colloidal matters and biological films (biofilm) may be referred to as "fouiants", and the process of the foulant build-up is referred to as "fouling".

Any process for preventing, limiting, inhibiting, removing and/or cleaning the foulant build up on the membrane may be referred to as "fouling control".

"Permeate" or "permeate water" may be used to include liquids, gasses, solids, particulate matter and/or colloidal matter which has been able to pass through or permeate through openings in an associated membrane.

Process fluids passing over the upstream side of a membrane gradually lose associated liquids and/or gaseous components by such components permeating through openings or pores in the membrane. The remaining process fluid generally becomes relatively thicker with a higher concentration of solids, colloidal matter and/or particulate matter which will not pass through openings or pores in the membrane. The accumulation of such materials on the upstream side of a membrane may be referred to as a "retentate" or "concentrated fluid".

The term "frame" may be used to describe any cassette, cartridge, chamber, supporting part, surrounding housing, frame assembly or any other structure suitable for holding a membrane or an array of membranes, together with any modifications of said frame for use in a particular filtration system, such as the filtration system of the present invention. Each flat sheet membrane or a bundle of hollow tubes, preferably arranged in a sheet like manner, may be referred to as "membrane element", and may include the housing of said membrane. Such an array or cluster of membrane elements may be referred to as "module" or "skein".

The term "vibration" may be used to describe the oscillating, reciprocating, or other periodic motion of a rigid or elastic body or surface or medium forced from a position or state of equilibrium. In other words it is a rapid oscillation of a particle, particles, or elastic solid or surface, back and forth across a central position. The present invention relates to membrane bioreactor ("MBR") method and a system that includes a vibration apparatus for reciprocating a membrane frame (or membrane housing/cassette) back and forth. The method/system minimizes the required air for air scouring. The applied HFPV on the membrane frame, creates high shear-rate forces acting on the membrane element, which removes foulants from the membrane surface.

The examined system includes at least a membrane frame/element containing membrane modules that are submerged in an MBR tank or in a separate cleaning tank. The membrane frame/element can be mechanically vibrated via high frequency ball vibrators, which enable the disclosed MBR system to be operated with higher flux, lower TMP as a result of lower fouling, than MBR systems using intense air scouring procedure. Various mechanical means can be employed to create the high frequency reciprocating motion such as pneumatic or electric vibrators. The method and system according to the present invention, works in situ at the relaxing intervals of the filtration process in a continuous or intermittent mode. The method demonstrates that there is no need of continuous use of HFPV process, as if a periodic vibration applied.

The inventor found out that the use of HFPV implementation in a membrane frame, particularly when the vibration implemented in short intervals of membrane relaxing period, is an extremely efficient, economic in the sense of reducing operating expenses, non destructive, energy efficient, safe, easily adjustable, relatively easy to install even in existing constructions, flexible, low maintenance, and easily scalable method to control fouling and eliminate phenomena of stacked thick layer of sludge in the form of cake or foulants onto membrane's surface, in membrane filtration systems.

Vibration HFPV technique/method can be applied mainly in the parallel or perpendicular direction of the membranes themselves or the surface of the array of membrane elements, at a displacement ranging from 0.1-1.5 mm, but also in other directions at a smaller displacement simultaneously. The HFPV implementation according to the present invention provides a homogeneous motion over the whole membrane surface and thereby controls the fouling by preventing and removing the foulant build-up, thus increasing membrane flux, decreasing TMP values, reducing the down time of operation, reducing the cleaning frequency of the membranes, reducing the energy cost and, therefore it can be mentioned that enhancing membrane lifetime and overall decreasing costs of the filtration process, which is of particular importance in large scale plants, such as waste water treatment plants.

The examined method must be beneficial for fouling control in large scale and/or continuous membrane filtration systems and even more suitable in combination with an advanced fully automated operating system probably a pic and a scada system, giving a better control to the end user by exploiting all the collected information (e.g. flux, temperature, MLSS, PH, TMP, ...) in order to use them as an input value for redefinition of the HFPV sizes or parameters for improvement of fouling removal and further optimization of the energy consumption. Membranes satisfactory for use with filtration systems incorporating specification and needs of the present invention may be formed from woven, non-woven materials and/or perforated plastic films, ceramic, nanomaterials, metal or perforated plates or any combination of them. Various types of membranes may be used based upon desired characteristics such as ability to separate liquids from gasses and the ability to separate suspended solids, colloidal matter and particulate matter from a fluid stream. Membrane materials may be selected with desired permeability or porosity for each application.

Moreover, various alternative embodiments of the present process invention, regarding biological treatment tanks. The method/system used in MBR tanks can be arranged as a treatment method together with anaerobic, anoxic, aerobic and amphoteric tanks.

Experimental setup for the different examples - Brief description of MBR pilot unit

The tests were performed in a continuous feeding operational mode in a pilot-scale MBR as illustrated in Fig. 1. For the operating needs of the pilot MBR unit, it was chosen to develop biomass using a new strong, in terms of organic load, Synthetic Waste Water (SWW). Activated sludge which obtained from a municipal wastewater plant was used to inoculate the pretreated biomass before it is used in the pilot unit. The final composition of the SWW was selected from the theoretical contribution of each element as COD/N/P and a series of laboratory tests was made to confirm the final features. Components for preparing the new SWW, shown in Table 1.

Table 1. SWW components

Concentration in SWW

Material * Chemical Formula

(mg/L)

D(+)-Glucose C6H12O6 H2O 400±10

Peptone A Peptone from soymeal 50±2

Peptone B Peptone from gelatin 150±5

Urea CO(NH₂)₂ 50±2

Ammonium Sulfate (NH₄)₂ S0₄ 50±2

Ammonium chloride NH4 CI 50±2

Potassium dihydrogen phosphate KH₂ P0₄ 15±1

* The synthesis of SWW supplemented with minerals and trace elements Membrane modules used in the pilot plant were both Hollow Fiber (HF) modules which were not production models, but special lab-made constructions adapted to our needs from known suppliers and Flat Sheet (FS) modules which were the smaller production models.

The HF membranes were prepared from polypropylene (PP) and Reinforced Polyvinylidene Fluoride (RPVDF). These lab-made membranes were used for experiments as shown in Figs. 3- 5. The FS membranes were prepared from Polyvinylidene Fluoride (PVDF). These membranes were used for experiments as shown in Fig. 6. Membrane elements were immersed in the MBR tank with a range of mixed liquor suspended solid (MLSS) concentration between 6,500-10,500 mg/l which was measured on-line while regular samples were taken to ensure the correct MLSS. Suction trans-membrane pressure (TMP) was adjusted between 0-300 mbar throughout the working life of the unit.

The pilot unit consists of two main parts. The first part of the pilot unit regulates continuously feed of SWW to the MBR unit. Concentrated SWW dosed at a constant rate, simultaneously with reverse osmosis water, to the preparation tank (1 ), in a batch process. Into the preparation tank the final dilution of SWW is achieved under low stirring. SWW is pumped to the MBR unit via an influent feeding line (2) under control by upper and lower level electrodes (57). For the protection of the installation from solids or aggregates bigger than 2 mm a strainer (3) placed on the end of the feed line. For the control of pH value, a dosing pump (5) through a feeding line (6) supplies NaHC0₃ solution from the storage tank (4).

As shown in Fig. 1 , the main body of the pilot unit consists of an amphoteric (8) compartment of 37 L in which a pH meter (60), a DO meter (58) and an MLSS meter (59) are placed for the on- line monitoring of the characteristics of biomass.

The necessary amount of air addition for the biological process to amphoteric (8) compartment, supplied by fine bubble diffusers (13), fed from a diaphragm type blower (9).

The second MBR compartment (7) consists of two more MBR compartments, one of 47L and another of 80L for HF & FS membrane modules, respectively.

Both MBR compartments are connected with (8) compartment and a sludge recirculation circuit. In the first compartment of (7) at least three HF membrane elements (15) are placed each one with a separate suction line (18) and in a set of three membrane elements, are connected in a common collector (22) with a suction pump. The same arrangement is also in the second compartment of FS membranes (16) (17) (21).

The permeate water from each line goes to effluent storage vessels (35) (36) (37) (38).

Through the HF or FS membranes, treated wastewater is intermittently permeated due to a partial vacuum, created by a suction pump (31 ) (32), which operates for 8 min and stops for 2 min. Each membrane is connected with an isolation valve, so that even if some of them fail, the others to continue operating.

That helps also in case of separate measurements in each membrane element. Further in each suction line (33) (34), it has been installed in series solenoid flow control valve (23) (24), glycerin pressure gauge (27) (28) and analog vacuum transmitter (25) (26).

Finally each suction line was provided with a flow meter (29) (30). Air scouring was performed by a diaphragm blower (10) which feed with air medium bubble diffusers (14). The air flow to each set of diffusers is regulated by regulator valves and flow meters (11 ) (12).

For the backwash of HF membranes a water storage vessel (39) together with a diaphragm pump (41 ) is installed which can start operating during relaxation with a time schedule given to the control station (54). In backwash line (40) there are installed in a series a flow control solenoid valve (44), a glycerin pressure gauge (43) and an analog pressure transmitter (42). Unit control station can be operated remotely via website and the installation is monitored by web cameras (56). The unit comprises also a PLC unit (53), a PC (55), electric board (52) and an odor air scrubber (61 ).

HFPV applied in membrane modules either in each membrane suction line or in a set of three lines. Pneumatic ball vibrator is fastened tight in order to provide shear forces through powerful vibration. The system consists of the vibration header/s (50) (51 ), air compressors (45) (46), feed air pipes (47), a flow control solenoid valve (48), regulation/control valves (49) and pressure measurement/control apparatus on compressors and in line before vibration header/s. Prior to isolation valve each suction line is equipped with an anti-vibration flex connector (19) (20) for limiting the transmission of vibration to the rest of the system.

Working principle of the vibrator is very simple (Fig. 2). Compressed air, drives an internal ball at high speeds around a highly finished and hardened steel race, creating high frequency vibration. Ball vibrator mounted directly to the structure so as to minimize energy loss. Since the creation of vibration based only on high speed rotation of the steel ball into the structure of the body, there are no complicated parts and suitable vibration adjustment can be made simply. Frequency and centrifugal force can be easily changed only by operating the pressure of compressed air.

Vibration experiments took place during relaxation either manually or via timer which controls the solenoid valve of compressed air supply. The vibration moves the membrane in a powerful way to all directions. Desired amplitude and frequency of vibration of each vibrator used may be adjusted either by the pressure and/or by means of compressed air flow to the vibrator. Vibration could be applied in a continuous or intermittent form.

During the experimental procedure, vibrator's frequencies according to the manufacturer were adjusted between 425 and 583 Hz (25.500-35.000 rpm) for the small vibrator (K8) and between 217 and 325 Hz (13.000-19.500 rpm) for the bigger vibrator (K16). Vibration amplitude was measured less than 1 mm in most cases. Vibration data as they are presented in Fig. 9-12 were confirmed with special measuring equipment (Laser Doppler vibrometer) in all type of experimental procedures. Vibration amplitudes (displacements) were measured optically by laser displacement sensor.

The Submerged Vibrated Membrane Bioreactors (SVMBR) during the experimental phase was operated under low air-scouring conditions and under constant flux, in order to achieve a realistic simulated level of fouling in a relatively short time. This choice was made to improve the filter's resistance to fouling in a process under little influence of membrane aeration, thus a small amount of air was provided, just for the upward movement of liquid in the membrane compartment. According to the manufacturer's instructions the membrane aeration rate for HF membranes should be 1 ,5-2 l/min for every membrane module. Throughout the duration of the experiments, system was supplied with less than 1 ,5-2 l/min of air for all the three membrane modules of each operating line so the air scouring flow was set to less than 1/3 of the manufacturer's instructions. Moreover no backwash procedure took place during HFPV experiments for HF or FS membranes except for the experiments in which backwash cleaning took place using adjustable temperature cleaning water, with or without vibration.

In the second compartment where FS membranes were installed, throughout the duration of the experiments, system was supplied with less than 3-5 l/min of air for the three membrane modules so the air scouring flow was set to less than 1/5-1/10 of the manufacturer's instructions which is 7-15 l/min pc.

All the measuring equipment was calibrated frequently in accordance with the manufacturer's instructions. The permeate flux was measured also very often with a volumetric tube. Long-term experiments have been carried out at different fluxes setup.

Through the present invention, without a doubt, several mechanisms to prevent the fouling mechanism are exhibited in a filtration process.

In the used high frequency ball vibrators as in all vibrators, there is a clear relationship of centrifugal force, the amplitude, and vibration speed. The centrifugal force Fc sets the membrane element and the frame to be vibrated, to vibration. The vibration width s (double amplitude) must be not too high in order to be useful and suitable for a scale up application, otherwise the equipment can be damaged.

This is the reason of use pneumatic ball vibrators in said invention experiments. Advantages of high frequency external vibrators are the small vibration amplitude at even increased frequency, in combination with compact size, easy application and low power consumption compared with the result obtained. Vibration frequency and centrifugal force are freely changeable by operation of air pressure (air flow volume).

Vibration energy has multiple effects upon exterior parts of a membrane. One cleaning effect includes reciprocating movement of outer portions of a membrane as represented in figs. 3 & 4 by arrows, in response to vibration energy directed generally parallel or perpendicular to the membrane element surface, depending on the vibrator's mode of installation. Also there is a second cleaning effect due to turbulent scouring of side faces.

This reciprocating motion on the one hand, especially because of increased acceleration of the mass of the membrane (see fig. 12), that causes a turbulent flow of fluid close to the membrane, and on the other hand the inertia of the particles and their interaction leads to detachment of these particles. That happens because process fluids contains, scale or solid particles, sludge cake or sludge film which are deposited on the surface of membrane element and due to their different rates of movement, during vibration implementation and induced movement most of these foulants removed. As an example due to the above described procedure when applying vibration to hollow fiber membranes, has been observed that while hollow fibers are fully stacked together because of deposits and sludge layer behaved as one body, then they retrieve almost their initial form with simultaneous improvement of flux and TMP.

Also this reciprocating movement of the vibrating membrane element, increases shear forces at the liquid-membrane surface. Depending on the vibration energy absorbers/materials that they are used most of the mechanical energy is transformed into shear-rate, which leads to removal of foulants from the membrane surface.

Another cleaning effect of reciprocating movement in hollow fiber membranes can be stated due to scraping of one another during HFPV implementation and especially when air scouring is applied also.

Filtration system as described in said invention may be used with closed housings having various configurations.

Most of the experiments under HFPV were handled during relaxation period, because according to the manufacturers all of the used "plastic" membranes need a small period of time for relaxation to recover their characteristics. Thus, for long time experiments, continuous filtration might have been catastrophic.

Direction of membranes during HFPV vibration is presented schematically in Figs. 3 and 4. Arrows a-b, c-d and e-f indicates an upwards - downwards motion, depending on the manner of vibrator installation, and show the general direction of a membrane element. As it is shown in aforementioned figures, the bigger size of the arrow indicates the bigger displacement relatively. As shown in Fig. 3 and 4, the system vibrates respectively to all directions in different amplitude.

When the vibrator is fasten in such a way that is parallel to the surface of the membrane (figs. 3&4) a vibration is occurred with the main motion in the direction a-b, a small motion in the direction c-d and a smaller motion in the direction e-f. Said vibration is generated by a high frequency pneumatic ball vibrator according to the operational air pressure.

Pressure is adjustable, so vibration parameters (frequency, amplitude etc.) are adjustable or constant in relation to the needs of the process. Vibration parameters can be adjustable or constant also when an electric vibrator is employed.

Said vibrator's frequency can vary in a range of 20-600 Hz, or 40-400 Hz, or 60-280 Hz, whilst system vibration frequency can vary in a range of 50-350 Hz, or 60-250 Hz, or 70-200 Hz, or 80-150 Hz. Related displacements (amplitude) according to our measurements can vary in a range of 0.1-1.1 mm which is related to the system, air pressure etc.

The examined method is suitable in combination with an advanced fully automated operating system as a pic and a scada system, giving a better control to the end user by exploiting all the collected information (e.g. flux, temperature, MLSS, PH, TMP, ...) in order to use them as an input value for redefinition of the HFPV sizes or parameters for improvement of fouling removal and further optimization of the energy consumption. Said operating system or control system, typically includes instruments/sensors at the MBR tank or in general to bioreactor as also to permeate side, to monitor and collect information on the actual filtration performance. Necessary instruments/sensors to permeate side, comprise permeate flow meters (as 29, 30) to measure the flow rate of permeate, pressure transmitters (as 25, 26) to measure the trans-membrane pressure (TMP), and turbidity sensor to meter the permeate quality.

Necessary instruments/sensors to MBR/Bioreactor side, comprise an MLSS sensor (as 59) to monitor suspended solids concentration, PH meter (as 60) together with temperature measurement in order to maintain a stable value to the bioreactor, a DO sensor (as 58) for controlling the dissolved oxygen concentration into the bioreactor.

The information provided by said control system with the aforementioned or even more sensors is collected by an automated operating system as a pic and a scada system (as 53-54). The control system processes the incoming signals - data and together with scada system, may apply in accordance with the user instructions, the appropriate HFPV parameters to said vibrators (as (50, 51) in response to the real filtration conditions. These vibration parameters should improve fouling control, which is confirmed in real time by said control system.

The main goal of this invention is to establish a method/system to prevent or to remove deposits from different filtration membranes used in a fluid separation process, by means of vibrators fastened either directly to the membranes or to the frame bearing said membranes, wherein the vibration applied in periods of membranes relaxing, which alternate with periods of active filtration, without vibration.

Vibration can take place mainly in a direction parallel or perpendicular to the surface of the membranes themselves or the surface of the array of membrane elements, at amplitude ranging from 0.1-1.5 mm. but also in other directions, at smaller amplitude. Preferably vibrator's frequency can vary in a range of 20-600 Hz, or 40-400 Hz, or 60-280 Hz, whilst system vibration frequency can vary in a range of 50-350 Hz, or 60-250 Hz, or 70-200 Hz, or 80-150 Hz, wherein the frequency, amplitude and/or waveform of the vibration can be constant or may be varied, during the membrane cleaning process and can be properly regulated according to the needs, with an advanced monitoring operational system.

Preferably, said variable vibration procedure is continuous during the membrane cleaning process, or intermittent according to the system needs.

In another embodiment, said cleaning procedure using vibration, takes place outside of the bioreactor in an external tank, using either clean water or permeate water coming from the filtration process, optionally in combination with chemicals. More preferably, said clean water or permeate water temperature is adjustable.

In yet another embodiment the method for fouling control of the present invention may also comprise membranes that are susceptible of backwash cleaning and clean or permeate water is pumped backwards through said membranes and said clean water or permeate water temperature is adjustable.

Another object of the present invention provides the need and use of an improved energy absorbing system or material to limit vibration energy losses. Vibration energy absorbing system/material may be placed at selected locations within a housing to prevent or minimize undesired return of vibration waves.

Preferably, said variable vibration procedure is generated by a pneumatic or electric vibrator.

Another object of the present invention provides an improved membrane filtration system or apparatus comprising system, wherein at least one diffuser for gas or liquid supply to the system is used, creating a scouring effect.

In another preferred embodiment of the method or system of the present invention, the membrane filtration elements are made of woven, non-woven materials and/or perforated plastic films, ceramic, nanomaterials, metal or perforated plates or any combination of them.

Said membrane filtration system comprises one or more hollow fiber or flat sheet membranes or plate and frame membranes which is susceptible of backwards cleaning, or a combination of them, or tubular modules, or capillary modules.

Also one of the aspects of the present invention includes removing or inhibiting build up of mineral scale, solids cake and/or biological films in such a way as not to be destructive to both the filtering element and the biomass itself.

It is a further object of this invention to provide an MBR system that does not utilize membrane air scouring as main cleaning process but as an associated cleaning system and process thus reducing energy consumption.

Another goal of the proposed method of this invention is to reduce the presence of dissolved oxygen in return activated sludge by minimizing the utilization of air scouring in membrane tank, thus allowing a recirculation of activated sludge with better characteristics from a membrane tank to an anoxic or anaerobic tank.

Another object of this invention through the adoption of the vibration method also is a further increment of the sludge concentration in bioreactor, so as to reduce even more the bioreactor volume and to reach higher efficiencies in biological nutrients removal.

In another embodiment of the present invention, the effects of vibration in means of turbulent flow of fluid close to the membrane, a submerged vibrator can be used to create a turbulent flow near the membrane which will increase shear stresses on the membrane surface.

The aforementioned has described rather broadly the most relevant and important features of the present invention, so that the detailed description of the invention that follows may be better understood and the present contribution to science may be better assessed. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. Should be estimated of the experienced in the art, that the conception and specific embodiment revealed, may be easily used as a basis for modifying or designing other structures for conducting the same purposes of the present invention. It should also be appreciated by experts to this technique that such equivalent constructions do not differ from the spirit and scope of the invention as is exposed in the attached claims.

The following examples are provided to illustrate hereinafter the invention. The details given in each example should not be perceived construed as limiting the field of this invention.

Example 1. Cleaning effect of HFPV vibration in a line using three HF membranes on a long - term filtration.

The effect of an HFPV vibration implementation on filtration performance was tested, in a line of three HF modules under constant flux mode. Fouling progress illustrated in fig. 5 in which we can see flux and TMP change over the operational time. During the whole operational period, the SMBR operated with an almost constant sub-critical flux mode, of about 5 l/m² h. In this case, TMP increased exponentially in the first two days from 7 to 40 mbar and from there to 70 mbar due to low air scouring and relative high flux adjustment (critical flux was about 6 l/m² h). In the next four days TMP increased very slowly (from 70 to 80 mbar), and then marginally up to 200 mbar, which was the set pressure operation limit, at day 19. Simultaneously, a significant reduction of flux at about 3 l/m² h was recorded, indicating that membrane fouling progressed with time. This was the first phase of the experiment.

Those data obtained under low membrane aeration mode in a set of three HF membranes and also in an almost constant temperature.

Under these conditions, an HFPV procedure took place with vibration schemes according to fig. 5, 6 & 7. Fig. 6, presents the second phase of the experiment, which shows clearly the effect of HFPV implementation, in a set of three membranes under steady flux mode, in terms of TMP and permeate flux versus time. In the first day of second phase (day 19) different vibrating types were applied following each other.

These vibration types were performed at intervals of one hour: a) type 1 -vibration implementation with a K8 vibrator working under air pressure (compressor gauge) of 7 bar for 5 minutes, b) type 2-vibration implementation with a K16 vibrator working under air pressure of 5 bar for 5 minutes, c) type 3-vibration implementation with a K 6 vibrator working under air pressure of 5 bar for 10 minutes. As it is obvious at the end of day 19, TMP is reduced dramatically (<100 mbar), while flux almost returned to initial values (5 - 6 l/m² h).

When the vibration was applied, shear enhanced by the vibration removes accumulated foulants. Results confirm that the HFPV vibration application is effective in removing fouling from membranes, in association with present invention. Moreover it is obvious that working in a low air-scouring mode in a percentage of 67% lower in relation to manufacturer's suggestions, basic objective of reducing energy consumption, achieved emphatically. This benefit of the reduction in energy consumption, on a large scale project acquires tremendous value and helps for accelerated depreciation of the initial investment.

Example 2. Effect of intermittent cycle

In order to examine the optimization of the performance over a significant period of time, we performed several tests by varying the intermittent cycles of implementation of vibration.

In fig. 6, beginning from day 20, the following vibration scheme was implemented (type 4), in order to examine the effect of intermittent implementation of vibration. Vibration type 4 uses a K16 vibrator working under air pressure of 5 bar for a period of 2 minutes. Initially vibration applied every 2 hours during the first day (day 20), then applied every 4 hours during the second day (day 21 ) and finally applied every 6 hours during the last day (day 22).

This experimental procedure demonstrates the successful impact of vibration scheme on maintaining TMP and flux values in a steady course with respect to the first day, giving a slightly increasing trend of TMP from day 20 to day 22. Figure 6 presents also the third phase of the experiment at which after day 22 when the vibration system stop working, a continuous deterioration of the filtration performance characteristics is presented to the end of day 29, in which the system reaches a steady fouling mode in a TMP value of 200 mbar, giving the same TMP versus time profile as presented in fig. 4 (day 13 - day 19).

Results confirm that the HFPV vibration has a fouling prevention effect on the membrane in association with present invention. These results confirm that intermittent HFPV vibration is an efficient method to conserve energy consumption in association with present invention. For all kind of vibration schemes, experiments show that the HFPV vibration provides a cleaning effect. The cleaning effect was extremely high so to drive TMP and flux values close to the initial and keep them at a constant level.

Example 3. The cleaning effect of an HFPV vibration on a pre-fouled FS membrane

In this experiment FS membranes were employed. As it is presented in fig. 8, during the operational period, the SMBR started operating with an almost constant sub-critical flux mode (critical flux was about 25 l/m² h), of about 18 l/m² h.

Figure 8, presents the three phases of the experiment, which shows the resulting data of TMP and permeate flux versus time. Those data obtained under low membrane aeration mode in a set of three FS membranes. Under these conditions, an HFPV procedure begins in day 37 with vibration schemes (VS.) also depicted in fig. 7. In the first phase of the experiment TMP was almost zero in the first fourteen days, then increased exponentially in the following five days (till day 20) from 15 to 50 mbar and thereafter, the fouling rate accelerated to produce a TMP value of 105 mbar (day 37).

Conversely there was a parallel reduction of flux at about 3.5 l/m² h, indicating that membrane fouling progressed with time. According to the photographs illustrating the state of the membranes before application of vibration, a permanent deposition of foulant material as a sludge cake layer was shaped between membranes (see the left photo fig. 7). This is the result of low amount of air scouring to the modules and thus justified the large decline in the flux. The TMP value of 100 mbar, was the set pressure operation limit, in this experimental design.

In the second phase of the experiment, two different vibrating types of HFPV implementation during the 37^th day are applied following each other. All vibration types were performed at intervals of one hour. The first one (between the 1^st and 2^nd vertical red line in fig. 7), type 1- vibration implementation with a K8 vibrator worked, under air pressure (compressor gauge) of 7 bar for 5 minutes, and results a decreasing trend of TMP and maintenance of flux values.

The second one (between the 2^nd and 3^rd vertical red line in fig. 7), type 2-vibration implementation with a K16 vibrator worked, under air pressure (compressor gauge) of 5 bar for 5 minutes. The results of this vibration shape are given in fig. 7. TMP values reduced significantly (<80 mbar), while flux was raised to 10 l/m² h.

This experimental procedure demonstrates the successful impact of vibration scheme, not only on maintaining TMP and flux values in a steady mode, but also demonstrates how helpful is to use this method for unblocking and cleaning of membrane elements from sludge cake deposition, where the air flow cannot reverse the condition of fouled elements. In the 2nd and 3rd photos in fig. 7, sludge cake breakage in the surface of the bioreactor and cleaned membranes are presented. This result confirms the ability of present invention to clean the fouled membrane in situ, without chemicals and labor costs.

The present invention comprises that contained in the attached claims, as well as those of the foregoing description. Even though this invention has been described as clear as it can be, prescribed also with certain examples, it is understood that the present invention of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention.

The method we presented is innovative as a "method", "system" and "work" in the following points:

1. The cleaning procedure via High Frequency Powerful Vibration (HFPV) in membrane modules is presented for the first time.

2. The use of pneumatic vibrators in MBR cleaning procedure is presented for the first time. The novelty of the presented HFPV method via pneumatic vibrators do not demand permanent installations and interactions, it is very safe since it uses no external moving parts, it requires no complicated electrical installation, it is much more easier in installation than others. Also it has compact size, easy application, low power consumption compared to other systems that have been presented and finally it can be applied to new or existing membrane systems with a few as possible technical modifications.

The novelty of the presented method consists additionally of the particular characteristics of vibration (small displacement, high acceleration, etc.) which fit to the design needs of the known membrane modules and do not appear in other works.

The novelty of the presented method using a pneumatic (or electric with similar characteristics of vibration) vibrator consists additionally of the particular range of vibration frequencies produced depending on the system needs, by a simple modification of the characteristics of compressed air feeding the vibrator. These characteristics can be constant or may be varied, during the membrane cleaning process and can be properly regulated according to the system needs, with an advanced monitoring system.

The experiments presented in this work were done over a long time in order to achieve a realistic simulation process in contrast to other works in this field.

Different - in power and other characteristics like frequency, displacement, acceleration, etc. - vibrators, different implemented vibration schemes and different membrane types were used and presented for the first time.

The HFPV via pneumatic vibrators take place mainly in a direction parallel or perpendicular to the surface of the membranes themselves or the surface of the array of membrane elements, at amplitude ranging from 0.1-1.5 mm, but also in all the other directions, at smaller amplitude, depending on the anti-vibration devices which are used. This is presented for the first time with these very promising characteristics.

HFPV experiments took place mainly during membrane relaxation period (all of the used "plastic" membranes need a small period of time for relaxation to recover their characteristics) either manually or via timer which controls the solenoid valve of compressed air supply and this is presented for the first time also.

Various vibrating schemes depending on time during relaxation period were used and conclusions were made about the effectiveness of each of them.

HFPV characteristics of the examined system measured accurately with special measuring equipment (Laser Doppler vibrometer). This is presented for the first time. The Submerged Membrane Bioreactor (SMBR), was operated under low air-scouring conditions; thus, a small amount of air was provided. This demonstrates the effectiveness of this method to reduce energy consumption required for air scouring of membranes and improves the method's resistance to fouling.

13. This established method to remove permanent and severe fouling deposits from membrane surfaces, by means of vibrators coupled either directly to the membranes or to the frame bearing, is presented successfully for the first time.

14. The cleaning procedure via HFPV is used directly on membrane modules without interrupting the continuous process of the MBR system.

15. The cleaning procedure for fouling control of the present invention comprise membranes that are susceptible of backwash cleaning in which clean or permeate water is pumped backwards through said membranes and said clean water or permeate water temperature is adjustable. This is presented for the first time. This established method is combined also with the HFPV vibration implementation.

DRAWINGS - FIGURES

For a better understanding of the nature and advantages of the invention may be acquired by referring to the description taken in conjunction with the accompanying drawings.

Legends of drawings - figures

Fig. 1 is a general process diagram illustrating the MBR pilot plant of the present invention. Fig. 2 is a general embodiment of a pneumatic ball vibrator illustrating the vibrator's working principle.

Fig. 3 presents a schematic overview of a filtration system using HFPV (pneumatic ball vibrator) technique on a HF membrane element.

Fig. 4 presents a schematic overview of a filtration system using HFPV (pneumatic ball vibrator) technique on a FS membrane element.

Figs. 5 - 7 show the effect of intermittent HFPV implementation in fouling progress in terms of TMP & flux over the operational time, in a set of three HF membranes.

Fig. 8 shows the effect of intermittent HFPV implementation, in a set of three FS membranes, in fouling progress in terms of TMP & flux over the operational time.

Fig. 9 presents the profile of the vibration velocity (RMS) during cleaning process in both HF & FS modules, using different vibrators, in different working pressure.

Fig. 10 presents the profile of the vibration frequency during cleaning process in both HF & FS modules, using different vibrators, in different working pressure.

Fig. 11 presents the profile of the vibration displacement during cleaning process in both HF & FS modules, using different vibrators, in different working pressure. Fig. 12 presents the profile of the vibration acceleration during cleaning process in both HF & FS modules, using different vibrators, in different working pressure.

Note: K8 & K16 are different type of ball vibrators. "-K" indicates HF membranes.

INDEX OF PARTS MENTIONED IN FIGURES

1. Influent preparing system 36. Effluent vessel II - Line 1

2. Influent feeding line 37. Effluent vessel I - Line 2

3. Solids strainer 38. Effluent vessel II - Line 2

4. NaHC0₃ solution storage tank 39. Backwash storage vessel

5. NaHC0₃ solution dosage pump 40. Backwash feeding line

6. NaHC0₃ solution feeding line 41. Backwash feeding pump

7. MBR compartment 42. Backwash line pressure transmitter

8. Amphoteric compartment 43. Backwash line pressure gauge

9. Aeration blower 44. Backwash line solenoid valve

10. Air scouring blower 45. Air compressor No1

11. Air scouring flow meter - Line 1 46. Air compressor No2

12. Air scouring flow meter - Line 2 47. Compressed air feeding line

13. Aeration diffusers 48. Compressed air solenoid valve

14. Air scouring diffusers 49. Air regulatory valves

15. Hollow fiber membrane elements 50. Ball vibrator - Type 1

16. Flat sheet membrane elements 51. Ball vibrator - Type 2

17. Membrane's suction lines - Line 1 52. Unit electrical panel

18. Membrane's suction lines - Line 2 53. Unit PLC

19. Anti-vibration flex connectors - Line 1 54. Control station - transmitter

20. Anti-vibration flex connectors - Line 2 55. PC

21. Permeate collector pipe - Line 1 56. Camera

22. Permeate collector pipe - Line 2 57. Level control electrodes

23. Solenoid valve - Line 1 58. DO sensor

24. Solenoid valve - Line 2 59. MLSS sensor

25. Pressure transmitter - Line 1 60. PH sensor

25. Pressure transmitter - Line 2 61. Odor air scrubber

27. Pressure gauge - Line 1

28. Pressure gauge - Line 2

29. Flow meter - Line 1

30. Flow meter - Line 2

31. Permeate suction pump - Line 1

32. Permeate suction pump - Line 2

33. Permeate suction Line 1

34. Permeate suction Line 1

35. Effluent vessel I - Line 1

Similar reference characters refer to similar parts throughout the several views of the drawings.

Claims

1. A method for fouling prevention or removal of deposits from filtration membranes used in a fluid separation process, by means of vibrators coupled either directly to the membranes or to the frame bearing said membranes, wherein:

• The vibrator frequency ranges from 20 to 600 Hz

• Vibration takes place mainly in a direction parallel to the surface of the membranes themselves or the surface of the array of membrane elements, at amplitude ranging from 0.1 -1.5 mm, but also in other directions, at smaller amplitude.

• The vibration takes parts in periods of relax of the membranes, which alternate with periods of active filtration, without vibration.

2. The method according to claim 1 wherein said method uses vibration frequency between 40-400 Hz

3. The method according to claim 1 wherein said method uses vibration frequency between 60-280 Hz

4. The method according to any of the preceding claims wherein the frequency, amplitude and/or waveform of the vibration are variable during the membrane cleaning process.

5. The method according to any of the preceding claims wherein said vibration during the membrane cleaning process is continuous.

6. The method according to any of the preceding claims wherein said vibration during the membrane cleaning process is intermittent.

7. The method according to any of the preceding claims, wherein said cleaning procedure using vibration takes place outside of the bioreactor in an external tank, using either clean water or permeate water coming from the filtration process, optionally in combination with chemicals.

8. A method according to claim 7, wherein said clean water or permeate water temperature is adjustable.

9. A method according to any of the preceding claims, wherein at least one of the membranes is susceptible of backwash cleaning and clean or permeate water is pumped backwards through said membrane where said water temperature is adjustable.

10. A filtration system including at least one filtration membrane in a fluid separation process having a permeate phase and a concentrated phase using vibrators comprising:

• A frame bearing at least one membrane element.

• A module housing said frames having at least one outlet for the permeate fluid.

• At least one tank in which the membranes will be immersed.

• At least one vibration energy source, to vibrate said module, wherein:

> The vibrator frequency ranges from 20 to 600 Hz

> Vibration takes place mainly in a direction parallel to the surface of the membranes themselves or the surface of the array of membrane elements, at an amplitude ranging from 0.1-0.5 mm, but also in other directions, at a smaller amplitude.

11. A filtration system according to claim 10, wherein an energy absorbing system or material is used.

12. A filtration system according to claims 10 & 1 1 , wherein at least one diffuser for gas or liquid supply to the system is used, creating a souring effect.

13. The method according to any of the claims 10-12 wherein said vibrators are pneumatic or electric.

14. The method according to any of the preceding claims 10-13, wherein said filtration elements are made of woven, non-woven materials and/or perforated plastic films, ceramics, nanomaterials, metal or perforated metal plates or any combination of them.

15. The system according to claims 10-14 wherein said membrane element comprises a hollow fiber or a flat sheet membrane or a plate and frame membrane, which is susceptible of backwards cleaning, or a combination of them, or a Tubular Module, or Capillary Modules.