A novel backwashing system for multi-media filters for reduced fluid consumption during backwashing

Abstract

The invention pertains to a novel backwashing system (10) for a multi-media filter (20) for reducing fluid consumption and hydraulic resistance during a backwashing procedure. The system (10) includes a filter vessel (20) that has a fluid inlet (30) and a fluid outlet (40). Granular filter layers (50A) to (50C) are located between the fluid inlet (30) and the fluid outlet (40). A bottom dispenser (60) is in fluid flow communication with a backwashing fluid supply (70). Supplementary dispensers (80A) to (80C), which are in fluid flow communication with a backwashing fluid supply (70), are arranged to locate within each granular filter layer (50A) to (50C). The system (10) is characterized by the backwashing of each of the granular filter layers (50A) to (50C) by means of the supplementary dispensers (80A) to (80C) along with backwashing of the entire filter vessel (20) in combination with the bottom dispenser (60).

Description

[0001] A NOVEL BACKWASHING SYSTEM FOR MULTI-MEDIA FILTERS FOR REDUCED FLUID CONSUMPTION DURING BACKWASHING FIELD OF THE INVENTION The present invention relates to a novel backwashing system for multi-media filters. More particularly, the invention relates to a system with horizontally arranged supplementary dispensers for backwashing procedures. The system further relates to a method of controlling a backwash procedure of a fluid treatment system to minimize the volume of fluid required for a backwash procedure. BACKGROUND TO THE INVENTION Multi-media filtration refers to a water treatment process that uses multiple layers of different filtration media to remove various contaminants or impurities from water. This type of filtration is commonly used in industrial, municipal, and commercial water treatment processes to produce water of a specific quality. As shown in Figure 1, a multi-media filter 1000 typically consists of a vertical column 1002, vessel, or tank containing several layers 1004a, 1004b, and 1004c of different materials. The materials are arranged based on their density and / or size, with the densest material 1004a at the bottom and the lightest (that is, least dense) material 1004c at the top. Typically, anthracite, sand, and garnet are used to form the different layers. Water flows through the multi-media filter 1000 from a top inlet 1006 to a bottom outlet 1008. As it passes through each layer 1004a to 1004c, contaminants or impurities of different sizes are trapped by the corresponding media. Thus, the media of each layer acts as a filter. Larger particles or impurities are captured in the top layers 1004c and 1004b, whilst finer particles or impurities are captured and / or trapped as the water moves downwards in the multi-media filter. Over time, the trapped contaminants or impurities causes the multi-media filter 1000 to clog. If clogged, the multi-media filter can no longer perform its filtering operation optimally. To clean a clogged multi-media filter, a process called backwashing is employed. During a backwash process, a large volume of water is forced at low pressure through a sparger 1010 and each layer 1004a to 1004c of the multi-media filter 1000 from the bottom (through the sparger 1010) to the top. In other words, the flow of fluid through the multi-media filter is reversed during a backwash procedure. By forcing a large volume of water through each layer 1004a to 1004c of the multi- media filter 1000, each layer 1004a to 1004c is fluidized to dislodge accumulated contaminants or impurities which were captured by the relevant layer. The dislodged contaminants or impurities are conveyed upwardly, through successive layers 1004a to 1004c of the multi-media filter 1000 and out of the multi-media filter 1000. In this manner, a multi-media filter 1000 can be unclogged. However, the backwashing process does come with its own set of challenges and disadvantages. Some of the main ones are: - Fluid consumption: One of the primary concerns with backwashing is the volume of fluid required. Especially in fluid-scarce areas, the amount of fluid used during backwashing can be wasteful and uneconomical. - Energy consumption: A backwashing procedure requires a pump or pumps to reverse the flow and increase the velocity of fluid to adequately clean the media. This process can consume significant energy, especially in large fluid treatment plants. - Potential media loss: If not conducted correctly, backwashing can lead to a loss of the filter media, especially if the backwash rate is too high. This can erode the media over time, necessitating more frequent media replacements. While backwashing is a necessary process to maintain a multi-media filter, the above- mentioned challenges and disadvantages underline the need for an improved system and method of backwashing a multi-media filter. OBJECT OF THE INVENTION It is therefore an object of the present invention to provide a novel backwashing system for multi-media filters and a method of controlling a backwash procedure of a multi- media filter which circumvents the above-mentioned disadvantages and / or provides a useful alternative to known backwashing systems, procedures, and methods of controlling a backwash procedure of a multimedia filter system. SUMMARY OF THE INVENTION According to a first aspect of the present invention, a novel backwashing system for a multi-media filter is provided for reducing fluid consumption during a backwashing procedure of the multi-media filter, wherein the system comprises: - a filter vessel having a fluid inlet at an operatively top region for supplying a fluid containing impurities to the filter vessel and a fluid outlet at an operatively bottom region of the filter vessel for conveying a filtered fluid out of the filter vessel; - granular filter layers which are disposed within the filter vessel and located between the fluid inlet and the fluid outlet, the granular filter layers serving to filter the impurities from the fluid; - a bottom dispenser that is in fluid flow communication with a backwashing fluid supply, the bottom dispenser being arranged at an operatively bottom region of the filter vessel; and - supplementary dispensers which are horizontally arranged to locate within each granular filter layer, wherein the supplementary dispensers are in fluid flow communication with a backwashing fluid supply and wherein they serve to introduce a backwashing fluid into each of the granular filter layers, wherein, the backwashing system is characterized by the backwashing of each of the granular filter layers independently by means of the horizontal supplementary dispensers, depending on the requirement of the granular filter layer, along with backwashing of the entire filter vessel in combination with the bottom dispenser to thereby reduce the consumption of backwashing fluid used during the backwashing procedure and a reduction of hydraulic resistance within the filter vessel. In another aspect of the present invention, the backwashing procedure induces fluidization of the granular filter layers to release trapped impurities within the filter layers. The impurities may be suspended particles in the fluid. The suspended particles may be silt, clay, grit, organic matter, algae and / or other microorganisms. However, it will be appreciated by the person skilled in the art that the impurities may be any particle or molecule which must be filtered from the fluid. For example, the impurities may also be fine ore materials, salts, and the like. The filter vessel may be a pressurized multi-media filter vessel. The multi-media filter vessel may include a base for supporting the filter vessel uprightly. That is, the multi- media filter vessel may be supported by the base such that the fluid outlet locates proximate the base, with the fluid inlet locating above the fluid outlet and the base. Thus, the multi-media filter vessel may take the form of a vertical shaft or column. It will be appreciated by the person skilled in the art that, during a backwash procedure of the system, the fluid inlet of the vessel may serve as a fluid outlet for the backwashing fluid. Similarly, during a backwash procedure of the system, the fluid outlet of the multi-media filter vessel may serve as a fluid inlet for the backwashing fluid. Alternatively, the backwashing system may also include a dedicated inlet for introducing the backwashing fluid into the multi-media filter vessel and a dedicated outlet for conveying the backwashing fluid together with the impurities out of the multi- media filter vessel. The bottom dispenser of the system may consist of a sparger, an annular rotating device, an underdrain, a lateral system comprising lateral pipes or channels that branch out from a central manifold, pulsators, and / or nozzle(s). The bottom dispenser is configured to distribute backwashing fluid evenly from the bottom region of the multi- media filter vessel and upwardly towards the top of the multi-media filter vessel. A plurality of granular filter layers may be provided within the multi-media filter vessel and between its fluid inlet and fluid outlet. For example, a first granular filter layer may be provided at an operatively bottom region of the multi-media filter vessel, a second granular filter layer may be provided to locate on top of the first granular filter layer, and a third granular filter layer may be provided to locate on top of the second granular filter layer. It will be appreciated by the person skilled in the art the more than three granular filter layers may be provided in the multi-media filter vessel. Each granular filter layer may comprise a particular granular filter media. That is, granular filter media of a first granular filter may be different to granular filter media of a second granular filter layer, and granular filter media of a third granular filter layer. Likewise, granular filter media of the second granular filter layer may be different to granular filter media of the first granular filter layer, and granular filter media of the third granular filter layer. The granular filter media of one granular filter layer differs from the granular filter media of another granular filter layer in terms of particle size and / or density. Examples of relevant filter media include anthracite, sand, garnet, gravel, activated carbon, ilmenite, magnetite, and crushed glass. A supplementary dispenser may be provided to locate within each of the granular filter layers for fluidizing and backwashing each granular filter layer from within and upwardly towards the fluid inlet of the multi-media filter vessel. The backwashing fluid inlet may supply the backwashing fluid to the bottom dispenser and the supplementary dispensers. Alternatively, the bottom dispenser and the supplementary dispensers may be connected to independent backwashing fluid supplies. The backwashing fluid supply may be connected to the fluid inlet. The backwashing fluid supply may include a pump for supplying the backwashing fluid at a pressure higher than ambient pressure to the bottom dispenser and the various supplementary dispensers. The supplementary dispensers may take the form of a sparger, an annular rotating device, pulsators, and / or nozzles. Each supplementary dispenser is configured to distribute the backwashing fluid from within a relevant granular filter layer and upwardly towards the fluid inlet of the multi-media filter vessel. In another aspect of the present invention, the novel backwashing system may include various sensors to monitor and / or control: - a flow rate of feed fluid which is to be filtered to the multi-media filter vessel; - a flow rate of a filtered fluid out of the multi-media filter vessel; - a flow rate of a backwashing fluid through the bottom dispenser and / or supplementary dispensers; - a flow rate of a fluid out of the multi-media filter vessel; - a pressure within the multi-media filter vessel (typically below and above a relevant granular filter layer); and - the temperature of backwashing fluid and / or a feed fluid which is to be filtered and / or a granular filter layer. Ideally, a bottom and a top pressure sensor are provided for each granular filter layer. For example, a first pressure sensor may be provided proximate an operatively bottom surface of the first granular filter layer and a second pressure sensor may be provided proximate an operatively top surface of the first granular filter layer. The first and second pressure sensors may then be used to calculate a pressure differential over the first granular filter media. The sensors may be electronic sensors that are configured to be in networked communication with a control system. Examples of relevant networked communications include the internet, a wired electronic connection, or a wireless electronic connection. In other words, the various sensors may be configured to receive from and send electronic communication signals to the control system. The backwashing system may include various valves for controlling the flow rates of fluids (that is, the fluid which is to be filtered and the backwashing fluid) to and from the multi-media filter vessel. A valve may be provided to control the flow of the backwashing fluid from the backwashing fluid supply to the bottom dispenser and / or the supplementary dispensers. The valves may include electronic sensors which are configured to be in networked communication with the control system. That is, the valves may be configured to receive from and send electronic communication signals to the control system. The valves may also be configured to be remotely operable from the control system. For example, the valves may include electronic actuation arrangements for closing and opening the valves electronically and remotely from the control system. Here, an electronic communication signal may be sent from the control room to the valves. In yet another aspect of the present invention the control system may comprise a computing environment that is configured to receive input signals (that is, electronic communication signals) from the sensors, perform calculations based on the received input signals, and provide output signals to the valves. The input signals and the output signals may be transmitted between the sensors, valves, and computing environment over a networked communication. The output signals typically take the form of electronic communication signals that are sent to the valves and configured to cause their electronic actuation arrangements to open or close the valves. The computing environment may include: - a communication module for receiving electronic communication signals from the sensors and valves and for sending electronic communication signals to the sensors and valves; - a storage module for storing computer readable instructions that pertain to the operation of the backwashing system; - a central processing unit for retrieving the computer readable instructions from the storage module and for processing the computer readable instructions to provide output data, wherein the output data takes the form of electronic communication signals to the sensors and valves. The output data may include an electronic communication signal to an electronic actuation arrangement of a valve. For example, the electronic communication signal may cause a valve to open or close, partially, or completely, to control the flow rate of a fluid through the valve and to or out of the multi-media filter vessel. The computing environment may also include input and output devices to permit a user of the computing environment to interact therewith and to control a method of operating the backwashing system and / or a method of controlling a backwashing procedure of the multi-media filter vessel. It will be appreciated by the person skilled in the art that the computing environment may be a physical or a virtual computing environment. According to another aspect of the present invention, there is provided a method of controlling a backwashing procedure of the backwashing system. The method includes the steps of: - measuring a differential pressure over a granular filter layer by comparing a pressure reading from a pressure sensor which locates proximate a bottom surface of the granular filter layer with a pressure reading from a pressure sensor which locates proximate a top surface of the granular filter layer; - comparing the measured differential pressure over the granular filter layer with a pre-defined maximum differential pressure over the granular filter layer and a pre-defined minimum differential pressure over the granular filter layer; - initiating the backwashing procedure of the system if the measured differential pressure over the granular filter layer is equal to or greater than the pre-defined maximum differential pressure over the granular filter layer; and - stopping the backwashing procedure of the backwashing system if the measured differential pressure over the granular filter layer is equal to or less than the pre-defined minimum pressure differential. The method may include the additional steps of recording a time when the backwashing procedure of the backwashing system is initiated, and recording a time when the backwashing procedure of the backwashing system is stopped. Before the backwashing procedure of the backwashing system (which includes the multi-media filter) is initiated, the method may include the step of closing a valve which controls the flow of the fluid which is to be filtered to the multi-media filter vessel. The backwashing procedure of the backwashing system may be initiated by opening a valve which controls the flow of the backwashing fluid from the backwashing fluid supply to the bottom dispenser and / or the supplementary dispensers. After the backwashing procedure of the backwashing system has been initiated, the method of controlling the backwashing procedure of the backwashing system may also include the additional steps of: - measuring a flow rate of the backwashing fluid out of the bottom dispenser and / or the supplementary dispensers by means of fluid flow sensors; - comparing the measured flow rate of the backwashing fluid with a pre-defined minimum backwashing fluid flow rate threshold and a pre-defined maximum backwashing fluid flow rate threshold; - decreasing the backwashing fluid flow rate through the bottom dispenser and / or the supplementary dispensers if the measured flow rate of the backwashing fluid is equal to or greater than the pre-defined maximum backwashing fluid flow rate threshold; and - increasing the backwashing fluid flow rate through the bottom dispenser and / or the supplementary dispenser if the measured flow rate of the backwashing fluid is equal to or less than the pre-defined minimum backwashing fluid flow rate. The backwashing fluid flow rate through the bottom dispenser and / or the supplementary dispensers may be decreased by closing a valve which controls the flow of the backwashing fluid from the backwashing fluid supply to the bottom dispenser and / or the supplementary dispensers. For example, the valve may be closed partially until the measured flow rate of the backwashing fluid is 20% below the pre-defined maximum backwashing fluid flow rate. Similarly, the backwashing fluid flow rate through the bottom dispenser and / or the supplementary dispensers may be increased by opening a valve which controls the flow of the backwashing fluid from the backwashing fluid supply to the bottom dispenser and / or the supplementary dispensers. For example, the valve may be opened partially until the measured flow rate of the backwashing fluid is 20% above the pre-defined minimum backwashing fluid flow rate. The method of controlling a backwashing procedure of backwashing system may be a computer-implemented method. That is, each step of the method may be performed and / or initiated within a computing environment. The computing environment may be the computing environment which forms part of the control system.

[0002] BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will now be described further, by way of non-limiting example only, and with reference to the accompany drawings, in which: Figure 1 is a schematic side view of a known backwashing system (prior art); Figure 2 is a schematic side view of a backwashing system according to one of the embodiments of the present invention; Figure 3 is a schematic side view of a second embodiment of the backwashing system of Figure 2 according to one of the embodiments of the present invention; Figure 4 is a schematic view of a third embodiment of the backwashing system of Figure 2 according to one of the embodiments of the present invention; Figure 5 is a schematic diagram of a computing environment that is in networked communication with the backwashing system of Figure 2 according to one of the embodiments of the present invention; Figure 6 is a process flow diagram showing steps of a method of controlling a backwashing procedure of the backwashing systems of Figures 2 to 4 according to one of the embodiments of the present invention; and Figure 7 is a second process flow diagram showing steps of a method of controlling a backwashing procedure of the backwashing systems of Figures 2 to 4 according to one of the embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION The present invention may be understood more readily by reference to the following detailed description of the invention taken in connection with the accompanying drawing figures, which forms a part of this disclosure. It is to be understood that this invention is not limited to the specific devices, methods, conditions, or parameters described and / or shown herein and that the terminology used herein is for the example only and is not intended to be limiting of the claimed invention. Also, as used in the specification including the appended claims, the singular forms ‘a’, ‘an’, and ‘the’ include the plural, and references to a particular numerical value includes at least that particular value unless the content clearly directs otherwise. Ranges may be expressed herein as from ‘about’ or ‘approximately’ another particular value when such a range is expressed another embodiment. Also, it will be understood that unless otherwise indicated, dimensions and material characteristics stated herein are by way of example rather than limitation and are for better understanding of sample embodiment of suitable utility, and variations outside of the stated values may also be within the scope of the invention depending upon the particular application. Embodiments will now be described in detail with reference to the accompanying drawings. To avoid unnecessarily obscuring the present disclosure, well-known features may not be described or substantially the same elements may not be redundantly described, for example. This is for ease of understanding. The following description is provided to enable those skilled in the art to fully understand the present disclosure and are in no way intended to limit the scope of the present disclosure as set forth. The embodiments described herein provide a novel backwashing system for multi- media filters for reduced fluid consumption during backwashing. It is pertinent to note that the fluid mentioned throughout the specification can be interchangeably referred to as water throughout. Further, the multi-media filtration described herein is the filtration using multiple filter media which can be collectively deduced as multiple-layer filtration using different media layers selected from filter sand, anthracite, granite, for the filtration and purification of fluid, e.g., water. Backwashing, as described herein, is the process of cleaning or washing the multi- media filter by reversing the flow of backwashing fluid with increased velocity and pressure to release the trapped impurities to be removed from the multimedia filter. Fluidization described herein is the process liquification of the granular filter layers in the multimedia filter to keep the solid particles floating in upward or reversed direction from the flow of the filtered fluid. According to an embodiment of the present invention, with reference to the drawings, in which like features are indicated by like numerals, a novel backwashing system for a multi-media filter according to the present invention is generally indicated by reference number 10. As best shown in Figures 2, 3 and 4, the backwashing system 10 includes: - a filter vessel 20 having a fluid inlet 30 at an operatively top region for supplying a fluid containing impurities to the filter vessel 20 and a fluid outlet 40 at an operatively bottom region of the filter vessel 20 for conveying a filtered fluid out of the filter vessel 20; - granular filter layers 50A, 50B, and 50C are disposed within the filter vessel 20 and located between the fluid inlet 30 and the fluid outlet 40, the granular filter layers 50A, 50B, and 50C serving to filter the impurities from the fluid; - a bottom dispenser 60 that is in fluid flow communication with a backwashing fluid supply 70, the bottom dispenser 60 being arranged at an operatively bottom region of the filter vessel 20; and - supplementary dispensers 80A, 80B, and 80C which are horizontally arranged to locate within each granular filter layers 50A, 50B, and 50C, wherein the supplementary dispensers 80A, 80B, and 80C are in fluid flow communication with a backwashing fluid supply 70 and wherein they serve to introduce a backwashing fluid into each of the granular filter layers 50A, 50B, and 50C, wherein the backwashing system 10 is characterized by the backwashing of each of the granular filter layers 50A, 50B, and 50C independently by means of the horizontal supplementary dispensers 80A, 80B, and 80C, depending on the requirements of the granular filter layers 50A, 50B, and 50C, along with backwashing of the entire filter vessel 20 in combination with the bottom dispenser 60 to thereby reduce the consumption of backwashing fluid used during a backwashing procedure and a reduction of hydraulic resistance within the filter vessel 20. The backwashing system 10 includes a fluid treatment system in the form of a multi- media filter vessel 20 for treating (that is, filtering) a fluid containing impurities. The impurities take the form of suspended solids and / or particles. The suspended solids and / or particles are typically silt, clay, grit, organic matter, algae and / or other microorganisms. The multi-media filter vessel 20 is a pressurized vessel and includes a base 20A for supporting the multi-media filter vessel 20 uprightly. That is, the multi-media filter vessel 20 is supported by the base 20A such that it takes the form of a vertical shaft. During normal operation of the multi-media filter vessel 20, fluid containing impurities is supplied to it through the fluid inlet 30. After the fluid has been filtered by the multi- media filter vessel 20, the filtered fluid is conveyed out of the multi-media filter vessel 20 by means of the fluid outlet 40. During a backwash procedure of the multi-media filter vessel 20, the fluid inlet 30 of the multi-media vessel 20 serves as a fluid outlet for the backwashing fluid. Similarly, during a backwash procedure of the multi-media filter vessel 20, the fluid outlet 40 of said multi-media filter vessel 20 serves as a fluid inlet for the backwashing fluid. As best shown in Figure 4, three separate granular filter layers 50A, 50B, and 50C are provided within the multi-media filter vessel 20. The three granular filter layers 50A to 50C are located on top of one another and between the fluid outlet 40 and the fluid inlet 30 of the multi-media filter vessel 20. The granular filter layers 50A to 50C serve to trap and filter the impurities from the untreated fluid to provide filtered or cleaned fluid. The first granular filter layer 50A is at an operatively bottom region of the multi- media filter vessel 20, the second granular filter layer 50B is on top of the first granular filter layer 50A, and the third granular filter layer 50C is on top the second granular filter layer 50C. Each granular filter layer 50A to 50C comprise granular filter media with densities and sizes that are different to the densities and sizes of the granular filter media comprising the other two granular filter layers. The granular filter media of the first granular filter layer 50A is denser than the granular filter media comprising the second 50B and the third 50C granular filter layers. The granular filter media of the third granular filter layer 50C has a lower density than the granular filter media comprising the first 50A and the second 50B granular filter layers. The granular filter media comprising the first granular filter layer 50A is also typically finer than the filter media comprising the second 50B and the third 50C granular filter layers. Similarly, the granular filter media comprising the third granular filter layer 50C is typically coarser than the granular filter media comprising the first 50A and the second 50B granular filter layers. The first granular filter layer 50A of the multi-media filter vessel 20 comprises garnet or gravel. Its small granules serve to trap and filter very fine impurities in the fluid which is to be treated. The second granular filter layer 50B of the multi-media filter vessel 20 comprises sand. The third granular filter layer 50C of the multi-media filter vessel 20 comprises anthracite. Its coarse granules serve to trap and filter impurities of a larger size (when compared to the sizes of impurities which are trapped and filtered in the first 50A and second 50B granular filter layers) in the fluid which is to be treated. The bottom dispenser 60 supplies the multi-media filter vessel 20 with the backwashing fluid for fluidizing the granular filter layers 50A to 50C during a backwash procedure of the multi-media filter vessel 20. The bottom dispenser 60 is a sparger that is configured to distribute the backwashing fluid evenly into a bottom region of the multi-media filter vessel 20 and upwardly towards the first granular filter layer 50A. The sparger 60 is in fluid flow communication with the fluid outlet 40 of the multi-media filter vessel 20 and the backwashing fluid supply 70. However, it will be appreciated by the person skilled in the art that the sparger 60 may be in fluid flow communication with a dedicated backwashing fluid outlet (not shown), which, in turn, is in fluid flow communication with the backwashing fluid supply 70. The backwashing fluid supply 70 includes a pump 72 that, during a backwash procedure, pumps the backwashing fluid from a container (not shown) to the fluid outlet 40 of the multi-media filter vessel 20 and through the sparger 60. The backwashing fluid is pumped to the sparger 60 at a pressure that is higher than the prevailing ambient pressure. Horizontally disposed supplementary dispensers 80A, 80B and 80C are provided to locate within each of the granular filter layers 50A, 50B and 50C.The supplementary dispensers 80A, 80B, and 80C are also in fluid flow communication with the backwashing fluid supply 70. During a backwash procedure, backwashing fluid is supplied to each granular filter layer 50A, 50B and 50C for fluidizing the granular filter layers 50A, 50B, and 50C by means of the supplementary dispensers 80A, 80B, and 80C. The supplementary dispensers 80A, 80B, and 80C includes nozzles and / or pulsators 82A, 82B, and 82C for distributing the backwashing fluid from within each granular filter layer 50A, 50B, and 50C and upwardly towards a top region of the multi- multi-media filter vessel 20. Sensors are provided in and around the multi-media filter vessel 20. The sensors include pressure sensors 92A, 92B, 92C, and 92D, temperature sensors (not shown), and flow rate sensors 94A, 94B, 94C, and 94D. The pressure sensor 92A to 94D monitors the pressure within the multi-media filter vessel 20 while the temperature sensor monitors the temperature of the backwashing fluid, fluid to be filtered and / or granular filter layer 50A to 50C. For each granular filter layer 50A, 50B and 50C there is provided at least one pressure sensor below and above the respective filter layer. The pressure sensors 92A, 92B, 92C and 92D calculates the pressure differential over granular filter layers 50A, 50B and 50C respectively. Various flow rate sensors 94A, 94B, 94C, and 94D are provided to monitor the flow rate of the backwashing fluid to the sparger 60 and / or the supplementary dispensers 80A, 80B and 80C. A flow rate sensor 94A is provided to monitor the flow rate of the backwashing fluid to the sparger 60. Flow rate sensor 94B monitors the flow rate of the backwashing fluid to the nozzle 82A of the first supplementary dispenser 80A. Flow rate sensor 94C monitors the flow rate of the backwashing fluid to the nozzle 82B of the second supplementary dispenser 80B. Flow rate sensor 94D monitors the flow rate of the backwashing fluid to the nozzle 82C of the third supplementary dispenser 80C. Flow rate sensor 100E is provided to measure the flow rate of a fluid which is to be filtered by the multi-media filter vessel 20. However, during a backwashing procedure of the multi-media filter vessel 20, flow rate sensor 100E is configured to measure the flow rate of the backwashing fluid out of the multi-media filter vessel 20. The sensors are electronic sensors that are configured to be in wireless networked communication with a control system (not shown). Valves for controlling the flow rates of fluids (that is, the fluid which is to be filtered and the backwashing fluid) to and from the multi-media filter vessel 20 are provided. At least one valve is provided within each pipe that conveys backwashing fluid to the sparger 60 and supplementary dispensers 80A to 80C. The valves 100A, 100B, 100C, and 100D are configured to be connected to the control system by means of a wireless networked communication. The valves 100A to 100D include an electronic actuation means (not shown) for closing and opening the valves 100A to 100D. The electronic actuation means of the valves 100A to 100D are configured to be operable from a control system 200. In other words, an electronic signal can be sent from the control system 200 to the valves 100A to 100D to close or open them so as to control the flow rate of the backwashing fluid therethrough. The control system 200 includes a computing environment 200. As shown in figure 5, the computing environment 200 includes: - a communication module 230 for receiving electronic communication signals from the sensors 92A to 92D, and 94A to 94D, and valves 100A to 100D and for sending electronic communication signals to the sensors 92A to 92D, and 94A to 94D, and valves 100A to 100D and / or their respective electronic actuation means; - a storage module 220 for storing computer readable instructions that pertain to the operation of the multi-media filter vessel 20; - a central processing unit 210 for retrieving the computer readable instructions from the storage module 220 and for processing the computer readable instructions together with the received electronic communication signals to provide output data, wherein the output data takes the form of electronic communication signals to the sensors 92A to 92D, and 94A to 94D, and valves 100A to 100D and / or to their respective electronic actuation means. The storage module 230 is any one or combinations of removable storage devices, non-removable storage devices, random access memory devices, read only memory devices, erasable programmable read-only memory devices, electrically erasable programmable read-only memory devices, flash memory devices, compact disc read- only memory devices, digital versatile disks or other optic disk storage devices, magnetic cassette devices, and magnetic disk storage devices. The communication module 230 includes a transceiver for transmitting and receiving electronic communication signals to and from the various sensors 92A to 92D, and 94A to 94D, and valves 100A to 100D, and / or their respective electronic actuation means. The electronic communication signals are sent over a wireless communication network (that is, an example of a networked communication). However, it will be appreciated by the person skilled in the art that any number of networked communication protocols could be used to establish an electronic communication network between the various sensors 92A to 92D, and 94A to 94D, and valves 100A to 100D of the multi-media filter vessel 20 and the computing environment 200. The central processing unit 210 is configured to retrieve the computer readable instructions from the storage module 220 and electronic communication signals received by the communication module 230 from the various sensors 92A to 92D, and 94A to 94D, and valves 100A to 100D of the multi-media filter vessel 20. Once retrieved, the central processing unit 210 is configured to process the electronic communication signals together with the computer readable instructions to provide output data. The output data takes the form of an electronic communication signal to an electronic actuation arrangement of one of the valves 100A to 100D of the multi- media filter vessel 20. The electronic communication signals cause the valves 100A to 100D to open or close partially or completely. In this manner, the flow rate of the backwashing fluid to the sparger 60 and / or the supplementary dispensers 80A to 80C can be controlled. This permits a user of the computing environment 200 to control a backwashing procedure of the multi-media filter vessel 20 remotely from the control system 200. The output data is an electronic communication signal to an electronic actuation arrangement of a valve 100. For example, the electronic communication signal causes a valve 100 to open or close, partially, or completely, to control the flow rate of a fluid through the valve 100 and to or out of the multi-media filter vessel 20. The computing environment 200 also includes input devices 240 and output devices 250 to permit a user of the computing environment 200 to interact therewith. This permits the user to initiate, control, monitor, and / or stop a backwashing procedure of the multi-media filter vessel 20. The computing environment 200 shown in Figure 5 is a physical computing environment. However, a person skilled in the art will appreciate that the computing environment 200 could also be a virtual computing environment. The computer readable instructions which are stored on the storage module 220 of the computing environment 200 are configured to permit the central processing unit 210 to compare different electronic communication signals received from the various sensors 92A to 92D, 94A to 94D, and valves 100A to 100D with one another. The electronic communication signals are typically readings or measurements taken by the various sensors 92A to 92D, 94A to 94D, and valves 100A to 100D of the multi-media filter vessel 20. The computer readable instructions are also configured to permit a user of the computing environment 200 to define various minimum and maximum parameters (for example, pressure losses, temperatures, fluid and backwashing fluid flow rates, and the like) within which the multi-media filter vessel 20 must operate. It will be appreciated by the person skilled in the art that these pre-defined parameters would be unique for each multi-media filter vessel 20. Furthermore, the pre-defined parameters may also be changed for a multi-media filter vessel 20 during its operational lifetime. This is because the pre-defined parameters are inherently dependent on a complex interplay of several factors. These factors include, but are not limited to: - the quality of inlet fluid which is to be filtered by the multi-media filter vessel 20; - the desired outlet quality of the fluid which has been filtered by the multi-media filter vessel 20; - the type (size, density, and / or chemical and / or biological inherent or reactive nature) of granular filter media used for the different granular filter layers of the multi-media filter vessel 20; - the number of granular filter layers in the multi-media filter vessel 20; - the pressure at which the fluid which is to be filtered by the multi-media filter vessel 20 is supplied to it; - the level of fouling or clogging of the granular filter layers of the multi-media filter vessel 20; and - the quality and type of backwashing fluid used during a backwashing procedure of the multi-media filter vessel 20. The computer readable instructions cause the central processing unit 210 to execute the steps shown in Figures 6 and 7. As shown in Figure 6, a method of controlling a backwashing procedure of the multi- media filter vessel 20 includes a first step 1000 of defining a maximum deferential pressure threshold (ΔPMAX) and a minimum differential threshold (ΔPMIN) for each, all, or some of the granular filter layers 50A to 50C. As previously explained, this is done by means of the input devices 240 of the computing environment 200. The maximum deferential pressure threshold (ΔPMAX) and the minimum differential threshold (ΔPMIN) values are stored on the storage module 220 of the computing environment 200. The method of controlling a backwashing procedure of the multi-media filter vessel 20 then includes a further step 2000 of measuring differential pressure (ΔPMEASURED) over the granular filter layers 50A to 50C. As shown in Figure 6, during a next step 3000A and 3000B, the central processing unit 210 compares the measured differential pressure (ΔPMEASURED) with the maximum deferential pressure threshold (ΔPMAX) and the minimum differential threshold (ΔPMIN) values which were stored on the storage module 220 of the computing environment 200. If the measured differential pressure (ΔPMEASURED) is equal to or greater than the pre- defined maximum differential pressure threshold (ΔPMAX), the method of controlling a backwashing procedure proceeds with a step 4000 of initiating the backwashing procedure. If the measured differential pressure (ΔPMEASURED) is equal to or less than the pre-defined minimum differential pressure threshold (ΔPMIN), then the method of controlling a backwashing procedure proceeds with a step 5000 of stopping the backwashing procedure of the multi-media filter vessel 20. The method also includes a further step 6000 of recording the time and date on which a backwashing procedure of the multi-media filter vessel 20 was initiated and / or stopped. As shown in Figure 7, the method of controlling a backwashing procedure of the multi- media filter vessel 20 also includes a further step 8000 of defining a minimum (ΔVMIN_THRESHOLD) and an entrainment (or maximum) (ΔVMAX_THRESHOLD) of a backwashing fluid flow rate through the sparger 60 and / or the supplementary dispensers 80A to 80C and out of their nozzles 82A to 82C. As previously explained, this is done by means of using the input devices 240 of the computing environment 200. The minimum (ΔVMIN_THRESHOLD) and entrainment (or maximum) (ΔVMAX_THRESHOLD) backwashing fluid flow rates are stored on the storage module 220 of the computing environment 200. As shown in Figure 7, during a nest step 10000A and 10000B, the central processing unit 210 compares the measured backwashing fluid flow rates (VMEASURED) with the minimum (ΔVMIN_THRESHOLD) and entrainment (or maximum) (ΔVMAX_THRESHOLD) backwashing fluid flow rates which were stored on the storage module 220 of the computing environment 200. If the measured backwashing fluid flow rates (VMEASURED) are equal to or less than the pre-defined minimum backwashing fluid flow rate (ΔVMIN_THRESHOLD), the method of controlling a backwashing procedure proceeds with a step 12000 of increasing the flow rate of the backwashing fluid flow rates through the sparger 60 and / or the supplementary dispensers 80A to 80C and out of their nozzles 82A to 82C. The backwashing fluid flow rates are increased until the measured backwashing fluid flow rates (VMEASURED) are 20% above the pre-defined minimum backwashing fluid flow rates (ΔVMIN_THRESHOLD). If the measured backwashing fluid flow rates (VMEASURED) are equal to or greater than the pre-defined entrainment (or maximum) backwashing fluid flow rates (ΔVMAX_THRESHOLD), then the method of controlling a backwashing procedure proceeds with a step 14000 of decreasing the flow rate of the backwashing fluid flow rates through the sparger 60 and / or the supplementary dispensers 80A to 80C and out of their nozzles 82A to 82C. The backwashing fluid flow rates are decreased until the measured backwashing fluid flow rates (VMEASURED) are 20% below the pre-defined entrainment (or maximum) backwashing fluid flow rates (ΔVMAX_THRESHOLD). AN EXAMPLE OF AN ADVANTAGE OF THE PRESENT INVENTION The below examples are provided to illustrate some of the advantages of the present invention. It should not be construed to limit the scope of the invention in any manner. One of the principal advantages of the present invention is that the multi-media filter vessel 20 of the present invention requires much less fluid during a backwashing procedure when compared to a backwashing procedure of a conventional or known multi-media filters. This advantage can be shown with reference to the multi-media filters shown in Figures 1, 2, 4 – that is, three different scenarios. A reduction of fluid required during a backwashing procedure of a multi-media filter vessel 20 can be estimated as a difference between fluid requirements for the first scenario, the second scenario, and the third scenario. This reduction in fluid can be calculated with the below equation: In the afore equation, V1 is the volume of fluid required to backwash a first multi-media filter and V2 is the volume of fluid required to backwash a second multi-media filter. For example, the volume of fluid required to backwash the multi-media filter 1000 shown in Figure 1 and the volume of fluid required to backwash the multi-media filter shown in Figure 2. To calculate the reduction of a volume of fluid required to backwash a multi-media filter, the following calculations and assumptions are also required: - monolayer (that is, a single granular filter layer) within the multi-media filter 1000 or 10; - the backwashing fluid flow rate through the sparger 1010 or 60 and the supplementary dispensers 80A to 80C must be selected; - the Reynolds number for each backwashing fluid flow must be calculated; - the porosity of the monolayer (that is, granular filter layers 50A to 50C) which has been fluidized during a backwashing procedure must be calculated; and - the height of the monolayer (that is, granular filter layers 50A to 50C) which has been fluidized during a backwashing procedure must be calculated. For all three different scenarios, the following assumptions were made: - the temperature throughout the multi-media filter is constant; - the density of fluid flowing into and out of the multi-media filter is constant (ρw = 1000 kg / m3); - the viscosity of the fluid flowing into and out of the multi-media filter is constant (µw= 1.0024·10-3Pa·s); - the granular particles of the mono filter layer are spherical particles (Φ = 1); - the porosity of the mono filter layer is 0.4 (ε0 = 0.4); - the diameter of all granular particles of the mono filter layer is the same (d0= 3 mm); - the diameter of the multi-media filter is 0.75 m; - the heigh (h0) of the mono filter layer is 1.4 m; and - the density of the granular particles (ρp) of the mono filter layer is 1500 kg / m3. The calculations referred to above are shown below with reference to each scenario. First scenario As shown in Figure 1, the multi-media filter 1000 of the first scenario is a conventional multi-media filter in that it includes a single sparger 1010 at a bottom region of the multi-media filter 1000 for introducing a backwashing fluid into the multi-media filter 1000. The mono granular filter layer comprises granular filter layers 1004a to 1004c. In this first scenario, it is assumed that: - the height (h0) of the mono granular filter layer is 1.4 m; and - the flow rate (V) of backwashing fluid to and from the sparger 1010 is 35 m3 / h. The cross-section (S) of the multi-media filter 1000 can be calculated as follows: The superficial velocity through the multi-media filter 1000 can be calculated as follows: The channel velocity can be calculated as follows: The Reynolds number can be estimated as follows: The Archimedes number can be calculated as follows: The porosity of the fluidized granular filter layer (that is, granular filter layers 1004a to 1004c, as a monolayer) can be calculated as follows: The heigh of the fluidized granular filter layer can be calculated as follows: The volume of the fluidized granular filter layer can be calculated as follows: The expansion coefficient can be calculated as follows: The volume of fluid required during a backwashing procedure of the multi-media filter 1000 shown in Figure 1 can then be calculated as follows: Second scenario As shown in Figure 2, the multi-media filter 10 of the second scenario includes a bottom dispenser in the form a sparger 60 and a supplementary dispenser 80A which is arranged to locate in granular filter layer 50A. The supplementary dispenser 80A distributes a backwashing fluid from within the granular filter layer and upwardly to fluidize the granular filter layer. The mono granular filter layer in this second scenario comprises granular filter layers 50A to 50C. In this second scenario, it is assumed that: - the height (h1) of the mono granular filter layer which locates below the supplementary dispenser 80A is 0.7 m; - the height (h2) of the mono granular filter layer which locates above the supplementary dispenser 80A is 0.7 m; - the flow rate (V1) of backwashing fluid to and from the sparger 60 is 17.5 m3 / h; and - the flow rate (V2) of backwashing fluid to and from the supplementary dispenser 80A is 17.5 m3 / h. Granular filter media of granular filter layer which locate below the supplementary fluid dispenser 80A means: The superficial velocity can be calculated as follows: The channel velocity can be calculated as follows: The Reynolds number can be estimated as follows: The porosity of the fluidized granular filter media can be calculated as follows: The heigh of the fluidized granular filter media can be calculated as follows: The volume of the fluidized granular filter media can be calculated as follows: Granular filter media of granular filter layer which locate above the supplementary fluid dispenser 80A means (without sparger 60): In the below calculations, the flow of backwashing fluid from below the supplementary dispenser 80A is excluded. Only the flow of backwashing fluid from the supplementary dispenser 80A is used. This permits one to assess the impact of the supplementary dispenser 80A on the granular filter media which is located above the nozzle 82A of the supplementary dispenser 80A. The superficial velocity can be calculated as follows: The channel velocity can be calculated as follows: The Reynolds number can be estimated as follows: The porosity of the fluidized granular filter media can be calculated as follows: The height of the fluidized granular filter media can be calculated as follows: The volume of the fluidized granular filter media can be calculated as follows: Granular filter media of granular filter layer which locate above the supplementary fluid dispenser 80A means (with sparger 60): In the below calculations, the flow of backwashing fluid from below the supplementary dispenser 80A (in other words, the flow of backwashing fluid from the sparger 60), together with the flow of backwashing fluid from the supplementary dispenser 80A are used. This permits one to assess the combined effect of the backwashing fluid flow from the sparger 60 and the supplementary dispenser 80A. Here, the following is assumed: The superficial velocity can be calculated as follows: The channel velocity can be calculated as follows: The Reynolds number can be estimated as follows: The porosity of the fluidized granular filter media can be calculated as follows: The heigh of the fluidized granular filter media can be calculated as follows: The volume of the fluidized granular filter media can be calculated as follows: Summary of the second scenario: Thus, the volume of fluid required to backwash the multi-media filter 10 shown in Figure 2 can be calculated as follows: The reduction in fluid required to backwash the multi-media filter 10 of Figure 2, when compared to that which is required to backwash the multi-media filter 1000 of Figure 1 can then be calculated as follows: Third scenario As shown in Figure 4, the multi-media filter 10 of the third scenario includes a bottom dispenser in the form a sparger 60 and three supplementary dispenser 80A to 80C which is arranged to locate in granular filter layers 50A to 50C. The supplementary dispensers 80A to 80C distributes a backwashing fluid from within the granular filter layers and upwardly to fluidize the granular filter layers. The mono granular filter layer in this third scenario comprises granular filter layers 50Ato 50C. In this third scenario, it is assumed that: - the height (h1) of the mono granular filter layer which locates below the first supplementary dispenser 80A is 0.5 m; - the height (h2) of the mono granular filter layer which locates between the first supplementary dispenser 80A and the second supplementary dispenser 80B is 0.5 m; - the height (h3) of the mono granular filter layer which locates above the third supplementary dispenser 80C is 0.4 m; - the flow rate (V1) of backwashing fluid to and from the first supplementary dispenser 80A is 11.67 m3 / h; - the flow rate (V2) of backwashing fluid to and from the second supplementary dispenser 80B is 11.67 m3 / h; and - the flow rate (V3) of backwashing fluid to and from the third supplementary dispenser 80C is 11.67 m3 / h. Granular filter media of granular filter layer which locate below the first supplementary dispenser 80A: The superficial velocity can be calculated as follows: The channel velocity can be calculated as follows: The Reynolds number can be estimated as follows: The porosity of the fluidized granular filter media can be calculated as follows: The heigh of the fluidized granular filter media can be calculated as follows: The volume of the fluidized granular filter media can be calculated as follows: Granular filter media of granular filter layer which locate below the second supplementary dispenser 80B (without sparger 60): In the below calculations, the flow of backwashing fluid from below the second supplementary dispenser 80B is excluded. Only the flow of backwashing fluid from the second supplementary dispenser 80B is used. This permits one to assess the impact of the second supplementary dispenser 80B on the granular filter media which locates above the nozzle 82B of the second supplementary dispenser 80B. The superficial velocity can be calculated as follows: The channel velocity can be calculated as follows: The Reynolds number can be estimated as follows: The porosity of the fluidized granular filter media can be calculated as follows: The heigh of the fluidized granular filter media can be calculated as follows: The volume of the fluidized granular filter media can be calculated as follows: Granular filter media of granular filter layer which locate below the second supplementary dispenser 80B (without sparger 60): In the below calculations, the flow of backwashing fluid from below the second supplementary dispenser 80B (in other words, the backwashing fluid from the sparger 60 and the first supplementary dispenser 80A) is included. This permits one to assess the combined effect of the backwashing fluid flow from the sparger 60, the first supplementary dispenser 80A, and the second supplementary dispenser 80B. In the below calculations, the flow of backwashing fluid from below the supplementary dispenser 80A (in other words, the flow of backwashing fluid from the sparger 60), together with the flow of backwashing fluid from the supplementary dispenser 80A are used. This permits one to assess the combined effect of the backwashing fluid flow from the sparger 60 and the supplementary dispenser 80A. Here, the following is assumed: The superficial velocity can be calculated as follows: The channel velocity can be calculated as follows: The Reynolds number can be estimated as follows: The porosity of the fluidized granular filter media can be calculated as follows: The heigh of the fluidized granular filter media can be calculated as follows: The volume of the fluidized granular filter media can be calculated as follows: Granular filter media of granular filter layer which locate below the third supplementary dispenser 80C (with sparger 60): In the below calculations, the flow of backwashing fluid from below the third supplementary dispenser 80C (in other words, the flow of backwashing fluid from the sparger 60 and that of the first- 80A and second supplementary dispenser 80B), are used. This permits one to assess the combined effect of the backwashing fluid flow from the sparger 60, first supplementary dispenser 80A, and the second supplementary dispenser 80B. Here, the following is assumed: The superficial velocity can be calculated as follows: The channel velocity can be calculated as follows: The Reynolds number can be estimated as follows: The porosity of the fluidized granular filter media can be calculated as follows: The heigh of the fluidized granular filter media can be calculated as follows: The volume of the fluidized granular filter media can be calculated as follows: Summary of the third scenario: Thus, the volume of fluid required to backwash the multi-media filter 10 shown in Figure 3 can be calculated as follows: The reduction in fluid required to backwash the multi-media filter 10 of Figure 3, when compared to that which is required to backwash the multi-media filter 1000 of Figure 1 can then be calculated as follows: As it is clear from the above calculations, the multimedia filter backwashing system and method of backwashing the system of the present invention has a distinct and surprising advantage over the prior art in that a volume of fluid which is required to backwash a multi-media filter is greatly reduced when compared to conventional fluid treatment systems and methods of backwashing such systems.

Claims

CLAIMS 1. A novel backwashing system for a multi-media filter is provided for reducing fluid consumption during a backwashing procedure of the multi-media filter, wherein the system comprises: - a filter vessel having a fluid inlet at an operatively top region for supplying a fluid containing impurities to the filter vessel and a fluid outlet at an operatively bottom region of the filter vessel for conveying a filtered fluid out of the filter vessel; - granular filter layers which are disposed within the filter vessel and located between the fluid inlet and the fluid outlet, the granular filter layers serving to filter the impurities from the fluid; - a bottom dispenser that is in fluid flow communication with a backwashing fluid supply, the bottom dispenser being arranged at an operatively bottom region of the filter vessel; and - supplementary dispensers which are horizontally arranged to locate within each granular filter layer, wherein the supplementary dispensers are in fluid flow communication with a backwashing fluid supply and wherein they serve to introduce a backwashing fluid into each of the granular filter layers, wherein, the backwashing system is characterized by the backwashing of each of the granular filter layers independently by means of the horizontal supplementary dispensers, depending on the requirement of the granular filter layer, along with backwashing of the entire filter vessel in combination with the bottom dispenser to thereby reduce the consumption of backwashing fluid usedduring a backwashing procedure and a reduction of hydraulic resistance within the filter vessel.

2. The backwashing system of claim 1, wherein the backwashing induces fluidization of the granular filter layers to release trapped impurities within the filter layers.

3. The backwashing system of claim 1, wherein the bottom dispenser consists of a sparger, an annular rotating device, an underdrain, a lateral system comprising lateral pipes or channels that branch out from a central manifold, pulsators, or a nozzle for distributing the fluid evenly from the bottom region of the filter vessel and upwardly towards a top of the filter vessel.

4. The backwashing system of claim 1, wherein a plurality of granular filter layers is provided within the filter vessel and arranged to locate between its fluid inlet and fluid outlet, and wherein each of the plurality of granular filter layers consists of granular filter media whose sizes and densities differ from granular filter media of other granular filter layers.

5. The backwashing system of claim 1, wherein a first supplementary dispenser locates within a first granular filter layer, a second supplementary dispenser locates within a second granular filter, and a third supplementary dispenser locates within a third granular filter layer.

6. The backwashing system of claim 5, wherein the first supplementary dispenser, the second supplementary dispenser, and the third supplementary dispenser consists of a sparger, an annular rotating device, pulsators, or a nozzle for distributing fluid from within a relevant granular filter layer and upwardly towards the fluid inlet of the filter vessel.

7. The backwashing system of claim 1, wherein the system further consists of sensors for monitoring the volume of backwashing fluid and its flow rates from the bottom dispenser and the supplementary dispensers and for measuring differential pressure over a granular filter layer of the system.

8. The backwashing system of claim 7, wherein the sensors are electronic sensors that are in networked communication with a computing environment.

9. The backwashing system of claim 1, wherein the system includes various valves for controlling a flow rate of a backwashing fluid from the bottom dispenser and the supplementary dispensers.

10. The backwashing system of claim 9, wherein the valves are electronic valves that include electronic actuation means, the electronic valves being in networked communication with a computing environment, and the electronic actuation means of the valves being configured to close and open the relevant valves upon receipt of an electronic communication signal from the computing environment.

11. The backwashing system of claim 10, wherein the computing environment includes: - a communication module for receiving electronic communication signals from electronic sensors and valves and for sending electronic communication signals to the sensors and valves; - a storage module for storing computer readable instructions that pertain to the operation of the backwashing system; and - a central processing unit for retrieving the computer readable instructions from the storage module and for processing the computer readable instructions to provide output data, wherein the output data takes the form of electronic communication signals to the sensors and valves.

12. A method of controlling a backwashing procedure of the system of claim 1, the method comprising the steps of: - measuring a differential pressure over a granular filter layer by comparing a pressure reading from a pressure sensor which locates proximate a bottom surface of the granular filter layer with a pressure reading from a pressure sensor which locates proximate a top surface of the granular filter layer; - comparing the measured differential pressure over the granular filter layer with a pre-defined maximum differential pressure over the granular filter layer and a pre-defined minimum differential pressure over the granular filter layer;- initiating the backwashing procedure of the system if the measured differential pressure over the granular filter layer is equal to or greater than the pre-defined maximum differential pressure over the granular filter layer; and - stopping the backwashing procedure of the system if the measured differential pressure over the granular filter layer is equal to or less than the pre-defined minimum pressure differential.

13. The method of claim 12, wherein the backwashing procedure of the system is initiated by opening a valve which controls flow of the backwashing fluid from the backwashing fluid supply to the bottom dispenser and the supplementary dispensers.

14. The method of claim 13, wherein, after the backwashing procedure of the system has been initiated, the method of controlling a backwashing procedure of the multi-media filter includes the additional steps of: - measuring a flow rate of the backwashing fluid out of the bottom dispenser and the supplementary dispensers by means of fluid flow sensors; - comparing the measured flow rate of the backwashing fluid with a pre- defined minimum backwashing fluid flow rate threshold and a pre- defined maximum backwashing fluid flow rate threshold; - decreasing the backwashing fluid flow rate through the bottom dispenser and the supplementary dispensers if the measured flow rate of thebackwashing fluid is equal to or greater than the pre-defined maximum backwashing fluid flow rate threshold; and - increasing the backwashing fluid flow rate through the bottom dispenser and the supplementary dispensers if the measured flow rate of the backwashing fluid is equal to or less than the pre-defined minimum backwashing fluid flow rate.

15. The method of claim 14, wherein the backwashing fluid flow rate through the bottom dispenser and the supplementary dispensers are decreased until it is 20% below the pre-defined maximum backwashing fluid flow rate.

16. The method of claim 14, wherein the fluidizing flow rate through the bottom dispenser and the supplementary dispensers are increased until it is 20% above the pre-defined minimum backwashing fluid flow rate.

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