MXPA99005490A - High rate filtration system - Google Patents

Abstract

A high rate, upflow filtration system is described in which a compressible, fibrous lump filtration media is compressed to adjust the porosity and collector size of the media in the bed and to provide a porosity gradient within the bed proceeding from more porous to less porous in a direction opposite to the flow of fluid so that filtration proceeds in a direction from a more porous to a less porous filter bed. Larger particles are removed by the more porous media and successively smaller particles are removed as the filter bed becomes less porous. The system is capable of reducing the turbidity of influent municipal wastewater from about 8 NTU to about 2 NTU at a wastewater flow rate of from about 820 to 1230 L/m2.min (20 to 30 gal/ft2.min), at a bed compression ratio of from about 15 to 40 percent, and at a backwash rate of from about 1 to 6 percent based on the total wastewater passing through the filter.

Description

HIGH SPEED FiLTRACiON SySTEM CROSS REFERENCE TO RELATED REQUEST This application is related to, and incorporates in the present for reference in its entirety, the co-pending common property application No. 60 / 032,643, filed on December 10, 1996 and reap the benefits of its previous filing date under 35 USC 119 (e).

FIELD OF THE INVENTION The invention relates to filtration systems, including filtration systems used in connection with the tertiary treatment of wastewater for the reduction of suspended solids.

BACKGROUND OF THE INVENTION The elimination and reuse of wastewater from untreated municipal wastewater is problematic. Strict wastewater treatment requirements have been enacted to protect human health, particularly in those areas that have a limited water supply or dense populations. For example, Title 22 of the California Administrative Code establishes strict water reuse criteria where human contact with treated wastewater is likely to occur. Typically, the wastewater is disinfected by chlorination or ultraviolet irradiation in places where the treated wastewater is discharged into surface waters inland. The disinfection of this type of wastewater typically achieves the complete destruction of pathogenic bacteria and the substantial deactivation of viruses, but does not provide complete destruction of the virus. Viruses have been detected in secondary effluents. Title 22 of the California Administrative Code is addressed to tertiary treatment requirements. Viral monitoring is not specified in title 22 because viruses typically occur at low concentrations in the treated wastewater. Virus monitoring is expensive. Viral tests require specific experience. Lab procedures are usually offline and time consuming. The analytical costs are high. Therefore, instead of imposing viral concentration measurements, Title 22 establishes a tertiary treatment system consisting of chemical coagulation, sedimentation, filtration and disinfection in places where the public may be exposed to treated wastewater. Tai like in a recreational dam. Normally, under the provisions of Title 22, the turbidity of the treated effluent can not exceed an average operating value of 2 NTU after fine filtration, and can not exceed more than 5 turbidity units more than 5 percent of the time during any period of 24 hours. Chlorination after this level of treatment typically ensures effective destruction of the virus sufficient for the protection of public health. Direct filtration with chemical addition is allowed as an alternative to the complete treatment systems specified in title 22 where it has been demonstrated that the results of the two treatment systems are comparable and meet the appropriate criteria. It has been determined that disinfection rates typically correlate well with residual particle size distributions and that the ability to inactivate an individual particle of wastewater is a function of particle size. Direct tertiary filtration by itself does not usually increase the rate of disinfection unless the particle size distribution in the sedimented wastewater is modified. Tertiary filtration systems that operate to remove large size particles should safely reduce the long contact times and high doses of chlorine typically used in wastewater recovery processes. Accordingly, a granular filtration medium is almost universally required as a part of the recovery of waste water. The granulated filtration is a bit slow and may be the limiting factor for a wastewater treatment system. Masuda and others, Patent E.U.A. No. 5,248,415 discloses an upflow filtering apparatus which is said to be useful as a tertiary filter for wastewater treatment systems and which operates at a relatively high flow rate. One embodiment of the present invention described in the Masuda patent is depicted in Figure 24 generally as 28 and is labeled as Background Art. The filtration medium described in the Masuda patent comprises a plurality of crimped fibrous lumps. The fibrous lumps are placed in a filtration apparatus with upward flow 28 between the first and second perforated panels 36 and 38, respectively. The wastewater flows upwards towards the fibrous lumps and the suspended matter is captured by the individual fibrous lumps. The first perforated panel 36 is fixedly mounted inside the apparatus and the second perforated panel 38 is movably mounted inside the apparatus and separated below the first perforated panel. The perforated lower moving panel 38, or lower plate, is raised to compress the fibrous lumps to eliminate air bubbles and to form a dense filter layer. The waste water passes up through the movable bottom plate and the filter layer and leaves the upper fixed plate 36. The fine solid materials in the upward flow adhere progressively to the filter layer from the lower portion to the upper portion of the filter. the same in that order. With the progressive filtration, the resistance to filtration is increased. The lower movable plate is lowered from time to time to define a cleaning chamber when the filtration performance is reduced and it is necessary to clean the fibrous lumps.

However, e! apparatus described in the patent Masuda et al., with the moving lower plate has some difficulties associated therewith. A ram or screw 40 for moving the lower plate passes through the waste water, the medium and the upper stationary plate 36. The screw decreases the amount of space available for the medium and potentialy causes some channeling through the medium in the region. of the screw. The medium is constructed of a loose fiber and can become entangled in the screw as it rotates. Where the screw passes through the top plate a seal is used, which further complicates the operation of the device. When the lower plate moves to compress the medium, the lower layers of the medium are compressed. The compressed filtration medium in the lower portion of the bed is then the first portion of the medium that comes into contact with the waste water since the filter is operated in an ascending manner. The filter is quickly clogged because both the large and fine particles are trapped by the compressed initial layers of the filtration medium. The entire unit is usually turned off before the upper filter layers are fully charged and the filter media is washed before the next cycle begins. The filter medium is washed by moving the bottom plate down away from the medium to define a cleaning chamber. However, the flow rate of the wash water makes it difficult to achieve separation between the medium and obtain efficient cleaning. The Masuda device typically requires frequent washing of the filtration medium at a full flow rate of wash water equivalent to the waste water flow rate. In this way the overall efficiency of the apparatus described in the Masuda patent is greatly reduced. It would be desirable to develop an appropriate filtration system for tertiary wastewater treatment that would substantially reduce or eliminate at least some of the problems associated with the Masuda device and yet provide a high speed filtration system as an appropriate alternative to the medium. of granulated filtration.

BRIEF DESCRIPTION OF THE INVENTION The invention provides a high-speed filtration system in which the size of the connector and the effective pore size of the filtration medium can be adjusted in accordance with the influent conditions and to promote efficient cleaning of the medium. The fluid travels through the successive layers of the filtration medium in which each layer becomes progressively more compressed with an effective pore size and smaller collector for filtration and removes small and large particles. The compression gradient promotes a more uniform charge of the medium through the filter bed. The compression gradient can be altered during filtration to adjust the pressure losses across the medium and to extend the filtration time while maintaining filtration efficiency within acceptable limits.

When used for sewage treatment, effluent turbidity values of 2 NTU or less can be achieved without the addition of chemicals for affluent turbidity values of up to approximately 8 NTU when the flow ranges from 820 to 1230 L / m2 * -min. with a bed compression ratio of 15 to 40%. AND! percentage of backwash water required at filtration rates of 820 and 1230 L / m2 »min. and at bed compression values of 20 and 30% is approximately 1 to 3%. Depending on the quality of the affluent material and the desired quality of effluent material, the filtration system of the invention must be operable at increased flow rates above 1230 L / m2"min. as long as the loss of load through the filter does not result in a non-economic operation. The flow rates of 1640 L / m2 * min. at 2050 L / m2 »min. or more should be useful, depending on the desired results. The filtration apparatus of the invention is suitable for a wide variety of fluid / solid separations, including the reduction of suspended solids in industrial and municipal wastewater, the recovery of working fluids from machine shops and a multitude of other separations. The filter media of compressible fibrous lumps as described in Masuda et al. Patent E.U.A. do not. 5,248,415 is contained between the upper and lower perforated panels in which, for operation in upflow mode, the upper panel or upper plate, is mobile in nature to adjust the porosity and the size of the collector of the medium. A porosity gradient is established along the filtration bed in which the porosity increases from the top to the bottom, or which is opposite to the flow direction of the fluid. The fluid to be filtered enters the filtration medium in the less compressed bottom in the upflow mode. The larger particles are trapped in the lower portion of the bed when the fluid enters. The smaller particles travel through the filtration medium to successive layers of the filtration medium. The final top layer of the filter media removes the smaller particles for which the filtration is provided. The compressed layer of the filtration medium in the upper part is clogged less frequently than when the lower layer of the filtration medium is compressed because the upper layer filters only the fine particles and not the large-sized particles additionally. The high speed filtration system of the invention typically is out of service less frequently and requires less washing of the medium than the previous apparatus. The filtration efficiency is comparable to that of the other filters but at filtration flow rates that are typically several times faster. There is no need to provide a seal on a top moving plate for a ram or screw that is designed to move the lower moving plate. The channeling can be reduced and the filtration bed is not interrupted. There are no mechanical means in which the medium could become entangled.

Multiple cells can be built in each of the filters that can be independently controlled so that one filter cell can be closed and cleaned while another is in operation. The washing cycle can be done at a relatively low flow rate with less water for recycling, which means that the process can be run efficiently. The foregoing and other objects, advantages and features of the invention, and the manner in which they are achieved, will be more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings, which illustrate the Preferred and example modalities, and in which: BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic drawing of a representative activated sludge plant including the tertiary treatment system according to the invention; Figure 2 is a partially cut away perspective view of a filtration apparatus according to the invention; Figures 3A to 3C are longitudinal cross-sectional diagrams showing the filtering apparatus of Figure 2 in three different modes of operation: Figure 3A represents an ascending filtration mode, Figure 3b represents an upward washing mode for cleaning the filtration means and Figure 3c depicts a rising jet wash mode for removing the remaining loose material from the filtration bed before starting a filtration mode; Figure 4 is a representation of a filtration means of the prior art for use in a filtration apparatus according to the invention as described herein; Figures 5A to 5D are graphs of effluent turbidity versus tributary turbidity for an apparatus of the invention operated at four different flow rates and four different compression grades of the filtration bed; Figure 6 is a graph of charge loss versus filtration flow rate for an apparatus of the invention, starting with a clean filtration bed, operated at four different compression rates of the filtration bed; Figure 7 is a graph of effluent turbidity versus tributary turbidity for an apparatus of the invention operated at 30% compression and at 2 different flow rates compared to several examples taken from the prior art operated at lower flow rates; Figures 8A to 23C are time graphs against 3 different parameters for evaluating the performance of a filtration apparatus according to the invention at 4 different influent flow rates and at 4 different percentages of compression of a filtration bed at a fixed initial depth for each flow velocity: Figures A are graphs of time versus effluent and effluent turbidity, Figures B are time graphs versus removal efficiency of suspended solids, and Figures C are time graphs against loss of charge across the filtration medium; and Figure 24 is a representation of the high-speed filtration system of the prior art described in Masuda and other U.S. Patent No. 5,248,415.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 a representative plant of activated sludge incorporating the filtration apparatus of the invention for the tertiary treatment of untreated municipal sewage for the increased removal of suspended solids is generally represented in highly schematic form. It will be recognized that the configuration of the activated sludge plant as it is represented is but an example of an activated sludge plant and that several alternatives are available. It should also be recognized that while the invention is described in the context of a tertiary treatment system for municipal sewage which is treated by an activated sludge process, the invention described herein is not limited in any way by the same. The invention is not limited to particular configurations or modes of operation of activated sludge plants, or to use in connection with an activated sludge plant. For example, the filtration apparatus of the invention can be used to treat wastewater that is not subject to sludge digestion. Where it is desired to use the wastewater due to its nutritional content, such as a fertilizer, then the waste water should be subjected to a primary clarification prior to filtration in an apparatus of the invention and in the absence of mud digestion. The wastewater can be examined and subjected to a vortex separator to remove large unsprung solids, including disposable cups, rags, panels, and other refuse, prior to filtration in an apparatus of the invention. The invention is not limited to the treatment of sewage or other industrial or municipal wastewater. In contrast, the invention described herein should normally be useful in connection with a wide variety of filtration processes in which solids of appropriate particle size for the effective pore size of the filtration medium are removed from fluids that are compatible with the environment, including both liquids and gases. For example, the filtration apparatus of the invention should be useful as a prefilter for removing small solid particles from seawater that could otherwise damage a reverse osmosis membrane in processes for the production of fresh water from salt water. The working fluids of machine shops, hydraulic fluids and various food or petroleum oils should be treated in a useful manner by the filtration apparatus of the invention in order to economically and efficiently remove small particles from them. Accordingly, while the invention will be described in detail in the context of the reduction of suspended solids in wastewater in connection with the activated sludge process, it should be understood that the detailed description is given solely for purposes of illustration and not as limitation. Various modifications and changes can be made and the invention is subject to a number of applications without departing from the scope of the invention as indicated in the appended claims. Returning to Figure 1 and the activated sludge plant represented at 50, the wastewater, including for example, untreated municipal sewage, is collected and pumped through a conduit 52 by a pump 54 to enter a sludge reactor. activated 56 for the digestion, by the biological sludge contained within the reactor, of organic carbonaceous compounds, nitrates and phosphates in a manner that is believed to be well known to those skilled in the art. The spent or excess mud is removed through a conduit 58 for disposal. The activated sludge reactor can be a single tank reactor in which the oxic, anoxic and anaerobic phases of the reaction can occur sequentially in the individual tank. These reactions can also take place in separate tanks. Mud digestion is sometimes referred to as a primary treatment of wastewater.

The mixture of activated sludge and treated waste water is then typically sent to one or more clarifiers 60 to remove the sludge by gravity from the residual treated water, which is sometimes referred to as a secondary treatment. The separated sludge is usually recycled from the clarifier to the activated sludge reactor through a conduit 62. The clarified effluent 64 is converted to the effluent wastewater for a tertiary treatment system if the tertiary treatment is used for a further reduction of the effluent. suspended solids. The high-speed up-filtration system of the invention shown at 66 is useful as a tertiary filtration system and receives as a tributary the secondary effluent 64 from a clarifier 60 for further reduction of suspended solids. The filtered effluent 67 from the high speed filtration system 66 can be further treated with chlorine or ultraviolet light, as necessary, and removed to a gully or reservoir of water. The filter 66 is washed from time to time with its own tributary received through the conduit 64, as described below, to clean the filter and remove the suspended solids trapped by the filter. Normally, the wash water will then be recycled through a conduit 68 to the effluent 52 to the activated sludge reactor and mixed therewith. A drain 70 is also provided on the filter, which usually drains into a culvert, should it become necessary to drain the filter out of the stream from the return conduit 68.

A filtration system of the invention is represented in a perspective view in section generally at 72, in Figure 2. The filtration system includes a housing 74 and a filtration bed 76 contained within the housing between two perforated plates, a plate upper mobile 78 and a fixed lower plate 80. The perforated plates contain a plurality of openings 82 through which waste water can enter and leave the filtration bed. The openings are dimensioned to allow waste water to freely enter and exit the filtration bed while substantially preventing the individual components of the filtration medium 84 from being displaced within the filtration bed. The individual components 84 of the filtration means are illustrated in an enlarged perspective view generally at 86. The top plate 78 is a vertically movable plate and its up and down movement is executed by a piston 88 positioned above the plate. The plate moves as much as necessary to control the degree of compression of the filter medium in the bed. As will be recognized by the person skilled in the art, the mechanism for moving the upper plate up and down can be designed to prevent it from extending substantially above the highest portion of the filter housing, which can reduce vertical space free necessary to accommodate the filter. The operation of the filter in several modes is shown in FIGS. 3A to 3C in a longitudinal cross-sectional plan through the filter housing 74. In the filtration mode, FIG. 3A, the filtration bed 76 is compressed by means of the upper moving plate 78, the effluent wastewater enters a distribution plenum 79 in the lowermost portion of the filter housing through a conduit 64. The wastewater, evenly distributed through the filtration bed through the plenum, travels up through the housing and enters the filtration bed 76 through the openings in the lower plate 80. E! Filtered wastewater effluent leaves the filtration stream through the openings in the upper plate and is transported out of the filtration housing through conduit 67. Suspended solids are trapped by the medium. It will be recognized that the channeling of residual water through the medium in the region of the wall of the housing, if present, can be lightened by supplying a flow distribution device adjacent to the wall of the apparatus to direct the flow of wastewater away from the wall and into the filtration bed. For example, a short screen may be adhered to the wall of the housing at regular intervals extending to the filter bed approximately 5.5 cm and at an angle of approximately 45 ° upward to direct the flow of waste water away from the wall and towards the filtration bed. When it is time to clean the filtration medium, the effluent duct 67 is closed and the duct 68 is opened (Figure 3B) to recycle the wastewater effluent from the filtration system to the activated sludge reactor 56 or another treatment site primary. The upper moving plate 78 moves vertically upwards to mechanically expand the filter bed towards an uncompressed condition. Air or other gas is injected below the filtration bed through conduits 92 and 94 (Figure 2) to help expand the bed and tangentially mechanically cut trapped solids from the filtration media. Typically, the air is injected first on one side and then on the other side of the filtration bed to increase the mechanical effect by alternating the injection of air between the conduits 92 and 94. After the filtration medium has been sufficiently cleaned, the The filter bed is flushed for an appropriate period to remove the residual solids prior to the re-start of the filtration (Figure 13). The filter bed is compressed as in the filtration mode and the air supply is turned off. However, in the jet wash mode, the jet wash water is supplied through the conduit 68 to the activated sludge reactor for further treatment rather than to be carried out through the effluent conduit 67. The main parameters that impact the filtration performance are the filtration speed, the depth of the medium, the size of the collector, the porosity and the quality of the tributary. Typically, the suspended solids in the effluent and effluent wastewater can be correlated to turbidity, as is well known to the person skilled in the art. The turbidity monitoring equipment can be used in a conventional manner, since it is believed that it is understood by the person skilled in the art, to determine the affluent turbidity and to compare the affluent turbidity with respect to the effluent turbidity so that it is monitored. the filter performance. The size of the collector and the porosity of the filtration medium, in particular, have an impact on the quality of the effluent water and the development of pressure loss through the filtration medium. Porosity is typically considered as the ratio, expressed as a percentage, of the voids, or interstices, of the filtration medium to the total volume of the filtration medium. The size of the collector is typically considered as the average diameter of the grains in the filtration bed in a typical filter that includes a granulated filtration medium. The size of the collector is usually defined as the average separation between the pores in the filtration bed. The fluid to be filtered flows around the filtration medium in conventional sand or anthracite filters that are used in connection with tertiary wastewater treatment. The filtration medium has been found useful in the practice of the invention in which fluid flows through the medium rather than around the medium, unlike conventional filtration media. The filter medium useful in the practice of the invention is also compressible, unlike conventional sand or anthracite media. The size of the collector and the porosity or vacuum ratio of the medium can be modified in accordance with the characteristics of the effluent wastewater because the filtration medium can be compressed. The porosity of the bed and the size of the collector of the medium is adjusted by adjusting the position of the movable upper plate. The porosity and collector size of the filtration medium can be altered during the filtration to overcome the effect on the effluent quality of the variations in the daily effluent water quality and to increase the useful life of the filtration media between the washing steps . The filtration bed can be mechanically expanded during filtration as the loss of charge develops without a loss of filtration efficiency. The loss of charge through the medium can be monitored using pressure sensor equipment as is known in the art. Countercurrent washing of the filter can be particularly efficient because the size of the filter bed and its porosity can be increased mechanically. The filtration medium has a low density, which is typically slightly above the density of the water. The porosity of the filtration medium is estimated to be about 80 to 90 percent and the porosity of the non-compacted filtration bed (Figure 3B) is about 92 to 94 percent. An example of a filter medium useful in the practice of the invention described herein is described in Masuda and other US Pat. do not. 5,248,415. This medium is depicted in Figure 4 hereof, generally at 30. The fibrous lumps have many crimped fibers in bundle 32, supplying synthetic fibers of 20 to 200 denier with two to ten crimps / 2.54 cm. The pack curled fibers are crushed and packed in the central portion thereof by a bonding wire 34. The pack curled fibers are rounded to provide the fibrous lump in the form of a sphere having a diameter of 10 to 50 mm. A fiber having a specific gravity higher than water, for example a polyvinylidene chloride fiber, is said to be optimal for the synthetic fiber to constitute the crimped fiber. The fibers can also be made from polyvinyl chloride, polyethylene fiber or some other synthetic fibers. A filter as described above was evaluated to determine a range of useful operating parameters by adjusting the compression degree of the filtration bed at various flow rates and considering the effluent and effluent turbidity, the removal efficiency for the removal of solids. suspended from the wastewater through the filter, and the development of pressure loss through the filtration bed. The test unit has the following characteristics as shown in table 1.

TABLE 1 ITEM UNIT VALUE Filter characteristics Global exterior Length m 0.85 Width m 0.74 Height m 3 Filtration area Length m 0.7 Width m 0.7 Area m2 0.49 Pipe Entrance mm 100 Filtered water outlet mm 150 Drain water outlet to mm countercurrent 150 Drain filter mm 100 Filter operation Nominal flow speeds L / min. 100-795 Nominal speeds of L / m2 * min. 205-1230 filtration Final maximum load loss Mm 2,540 Nominal wash speed at L / m2. min 410 countercurrent The effluent turbidity was plotted against the affluent turbidity in a series of 16 runs at four different filtration rates and four different compression levels of the filtration bed. The speeds of filtration ranged from 205 to 1230 L / m2 »min. and compression speeds They varied from 0 to 40 percent compression to assess the effluent and effluent turbidity, the loss of charge through the filtration media and the fractional turbidity removal based on the effluent and effluent turbidity. The non-compacted filtration bed at 0 percent compression was approximately 760 mm deep. The filtration rates, the compression levels and the depths of the medium for each run are summarized in Table 2.

TABLE 2 Running Speed no. filtration Depth Ratio Porosity compression of the medium IJm2 »min. estimated% 1 205 0 760 92 2 205 15 650 90.5 3 205 30 530 88.5 4 205 40 460 87 5 410 0 760 92 6 410 15 650 90.5 7 410 30 530 88.5 8 410 40 460 87 9 820 0 760 92 10 820 15 650 90.5 11 820 30 530 88.5 12 820 40 460 87 13 1230 0 760 92 14 1230 15 650 90.5 15 1230 30 530 88.5 16 1230 40 460 87 The countercurrent wash flow rate for the filtration unit was adjusted in a conventional manner using a bypass loop located in the supply tributary of the conduit to the filtration unit. The bypass loop was equipped with a ball valve that was used to regulate the countercurrent flow rate. The tributary conduit was equipped with a gate valve followed by an automatic ball valve opposite the bypass loop. The gate valve was used to regulate the filtration rate and the automatic ball valve was used to divert the flow to the bypass loop where the countercurrent wash flow rate could be adjusted as soon as the wash cycle started. countercurrent The countercurrent wash flow rate was adjusted to approximately 410 L / m2 »min. for all 16 runs. A terminal load loss value of 2540 mm of water was selected for all runs. Sampling for turbidity was achieved at approximately 400ml / min for all runs. Suspended solids were correlated to the turbidity values in accordance with standard methods recognized in the art. The results of the 16 runs are plotted in Figures 8A to 23C. Figures A are graphs of affluent turbidity and effluent against time. Figures B are graphs of efficiency of removal of suspended solids (turbidity) against time. Fractional turbidity versus time removal was obtained using the effluent and effluent turbidity values obtained in Figures A and with respect to the following relationship: removal efficiency = 1 - (effluent / tributary turbidity). The initial head loss and the development of pressure loss through the filtration medium was continuously monitored. The results are plotted in figures C for figures 8 through 23.

Figures 8 to 11 are for the filtration of waste water at a speed of 205 L / m2 »min. Figure 8 shows an initial depth of the bed of 760 mm with 0 percent compression. Figure 9 is at 15 percent compression; Figure 10 is at 30 percent compression; and Figure 11 is at 40 percent compression. Figures 12 to 15 are at a filtration rate of 410 L / m2 »min. to four different bed compressions of 0 percent, 15 percent, 30 percent and 40 percent. Figures 16 to 19 are taken at a filtration rate of 820 L / m2 »min at four different bed compressions of 0 percent, 15 percent, 30 percent and 40 percent. Figures 20 to 23 are taken at 1230 L / m2 »min at four different bed compressions of 0 percent, 15 percent, 30 percent and 40 percent. In these figures it is shown that as the degree of compression of the bed increases, the overall removal of turbidity also increases. Indeed, at a low flow rate of 205 L / m 2 »min, the filter was tearing and the flow occurred primarily around the filtration medium instead of through it as is the case with the high filtration rates. The removal efficiency is reduced when the flow is around the filtration medium because the suspended solids and liquid can move through the relatively large interstices between the individual filter lumps. However, as the material begins to accumulate within the filtration bed and participate in the filtration, the removal efficiency increases. The tearing is not as significant as at high filtration rates because the removal of suspended solids occurs primarily through the filtration medium and not around it. When the flow is through the filtration medium, the size of the collector, which can be defined as the size of the grains in a granulated filtration medium, can be defined with the filter medium as used in the invention as the average pore separation between the structure of the individual filtering clod. The trapped particles tend to decrease the size of the collector of the filtration medium and result in an increase in the removal of additional particles by interception and infiltration. When the flow is around the filtration medium, the collector size is defined as the nominal diameter of a fibrous lump. The difference between the initial size of the collector and the size of the collector at any time during the filtration cycle is much greater than when the flow occurs around the medium, and therefore the tearing of the filter becomes more important at filtration rates low. The porosity, depth of the filtration bed and the size of the collector can all be altered, even during the filtration cycle, because the filtration medium can be compressed. The maximum removal efficiency that could be achieved is somewhat dependent on the characteristics of the material being filtered, which is primarily colloidal. The removal efficiency typically increases as the filtration bed is compressed until some maximum level is reached. For example, as shown in Figures 8B through 11 B, the average filter removal efficiency increased from 55% with a bed compression ratio of 0% to approximately 61% with a bed compression of 30% when the flow rate was 205 L / m2 »min. At 410 L / m2 »min, filter removal efficiency increased from 48% to 0% bed compression to 65% with 30% bed compression. The maximum removal efficiency in the practice of the invention is presented at different levels of compression as the filtration rate increases and the characteristics of the tributary to the filter change. It was observed that the maximum removal efficiency is presented at 40% compression of the bed at a filtration rate of 410 Um »min however, at flow rates of 820 to 1230 L / m2» min, the maximum removal efficiency is I present at a bed compression of 30%. It should be recognized that the filtration system of the invention can be operated usefully at flow rates above 1230 L / m2 »min depending on the quality of the tributary, the desired quality of the effluent and the loss of load through the filter. For example, if the effluent is to retain some nutrient quality to be used as a fertilizer, then the filter affluent is typically taken from a primary clarifier. Depending on the quality of the effluent and the desired quality of the effluent, the filter must be operable at increased flow rates above 1230 L / m2 »min while the increase in the velocity of head loss around the filter provides an operation economic Flow rates of approximately 1640 L / m2 »min to 2050 L / m2» min should be useful in this regard. As shown in Figures 8B through 23B, the removal efficiency is not significantly influenced by the filtration rate. In contrast, the removal efficiency is more impacted by the compression of the filtration medium. It should be noted that the removal efficiency appears to be lower when the affluent turbidity is in the range of 1.5 to 3 NTU. At low affluent turbidity, the particle size of the tributary solids is more displaced towards smaller particles of colloidal character than the typical particle size distribution observed when the tributary turbidity is greater than 3 NTU. The turbidity of the secondary effluent from a typical activated sludge wastewater treatment plant is in the range of 3 to 8 NTU. Accordingly, in the case where the turbidity is in the range of 1.5 to less about 3 NTU, the filter performance can not be evaluated solely on the basis of the removal efficiency data. An effluent turbidity versus tributary turbidity analysis was performed to determine the various effluent turbidity values that can be filtered with the filter of the invention without the use of chemical products and without exceeding an effluent turbidity value of 2 NTU, which is the current requirement under title 22 of the California Administrative Code.

The results of the analysis are plotted in Figures 5A to 5D at four different filtration rates from 250 to 1230 L / m2 »min. As shown in Figures 5A to 5D, the required effluent turbidity values can be achieved by increasing the influent turbidity as the compression of the filtration bed increases at all the filtration rates evaluated. It was determined, by evaluation, that the effluent turbidity is typically equal to or less than 2 NTU for affluent turbidity values of up to 8 NTU when the flow velocity ranges from 410 to 1230 L / m2 »min. If the affluent turbidity is from 7 to 10 NTU, then chemical addition is normally required to produce an effluent with an average turbidity of 2 NTU or less. It should be noted that this performance in terms of the effluent and effluent turbidity values is comparable to the operation of conventional filters, as reflected in Figure 7. The main types of conventional filtration technologies include 1) flow filters descending with individual filtration media, dual filtration media and conventional multiple filtration media, 2) filters with individual deep bed media with downflow and / or upflow, 3) downflow filters with individual filtration media after the filtration bed, 4) downflow transfer bridge filters with shallow individual and dual filtration media and 5) deep bed filters with individual non-statified filtration media with up-flow of continuous counter-current washing. However, the filter as described herein achieves these performance levels at filtration rates that vary from 6 to 15 times more than those for conventional filters. In this way, the overall efficiency of the filtration obtained with the practice of the invention is several times greater than with conventional filters. The clean filter head loss, the development of pressure loss during filtration and the development of load loss with the accumulation of solids are affected by the filtration rate and bed compression. The clean filter head loss was plotted against the filtration rate for the four filtration rates that were evaluated at four different bed compressions in Figure 6. As shown in Figure 6, the initial head loss at a flow rate of 205 L / m2 »min and 0% bed compression is 63 mm of water. This initial value increases linearly to a value of 127 mm of water at a flow rate of 410 L / m2 »min at 0% compression. The linear increase in head loss tends to indicate that the flow rate through the flow is laminar. The impact of the bed compression is clearly evident in the curves plotted in Figure 6. However, the increase in pressure loss at any given filtration porosity is not a linear function of the compression degree. Increasing the degree of bed compression increases both the removal efficiency and the load loss that occurs through the filtration medium. Therefore, it is important to identify a level of compression in which the desired effluent quality is achieved while maintaining the loss of charge that occurs through the filtration medium within reasonable levels. The development of charge loss as a function of time for the different filtration rates and the compression values of the bed is illustrated in Figures 8C to 23C. As shown in these figures, depending on the filtration rate, there is a gradual accumulation of load loss as a function of time as the suspended solids accumulate inside the filter. At some critical point, the pressure drop begins to increase linearly curved which is characteristic of the infiltration removal. The relationship of the development of charge loss through the filtration medium to the accumulation of suspended solids in the medium was evaluated in the following manner. The accumulation of suspended solids in the filtration medium was calculated using the effluent / effluent turbidity data versus time shown in Figures 8A through 23A and the following mathematical relationship Suspended solids (g / L) = 0.0023 x Turbidity (NTU) Accumulation of suspended solids in the filtration medium at any time is calculated by the following mass balance equation SSac (f0.0023? T Q l = t? T ftuAafl-Turbefi ii where SSacc = accumulation of suspended solids at time t, g / m3 Q = filtration rate, L / min V = volume of filtration medium, m3? t = frequency of data collection, Turbafi min = affluent turbidity, NTU Turben = effluent turbidity, NTU i = time index of collected data The development of load loss as a function of time is shown in figures 8B a 23B The corresponding development of head loss based on the amount of suspended solids retained within the filter is shown in Figures 8C to 23C It is also important to evaluate the amount of backwashing water that is used in relation to the amount of processed water to determine the efficiency of the filter Table 3 shows the summary data of the operation of the filter as described, including backwashing, water use and water production.

TABLE 3 Filtration water speed filtration Ratio of total water Corrida to compression produced. do not. countercurrent% L / m2 -min% L / m2 »d 1 205 0 4.1 289,000 2 205 15 4.1 289,000 3 205 30 4.1 289,000 4 205 40 4.1 289,000 5 410 0 2.1 578,000 6 410 15 2.1 578,000 7 410 30 2.1 578,000 8 410 40 3.1 572,000 9 820 0 1.1 1,156,200 10 820 15 1.7 1,139,800 11 820 30 2.0 1,131,600 12 820 40 2.8 1,115,200 13 1,230 0 1.8 1,685,100 14 1,230 15 1.8 1,672,800 15 1,230 30 3.1 1,629,750 16 1,230 40 5.4 1,500,600 The secondary effluent, which is used as the tributary for the tertiary wastewater treatment filter, can be used as countercurrent washing water. It was observed that a backwashing rate of 410 L / m2 »min. It was enough to clean the filtration medium. The cleaning operation of the filtration medium took approximately 30 minutes, although shorter countercurrent washing cycle times can be achieved. The percentage of total water used to backwash the filter, as summarized in Table 3, was calculated using the following expression: Wash water 0 _ W | B x 100 countercurrent, wF + wB where WB = water used to backwash the filter WF = Total filtered water The ability to reduce the amount of backwash water has significant cost implications with respect to the sizing of the wastewater treatment process. The typical backwash percentage for most conventional effluent filters ranges from 6 to 15%, so that significant savings are achieved by practicing the invention described herein. It should be noted that the filtration apparatus described in Masuda and other US patent. do not. 5,248,415 typically required washing the filter media frequently at a full flow rate equivalent to the flow rate of the wastewater. The filtration system described herein was evaluated with respect to the amount of water produced per day. Taking into account the water used for backwashing, the water production velocity was reported for different filtration rates and various compression ratios of the bed in the last two columns of table 3. As shown, it is possible to produce 1 , 672,800 Um2 »day at a filtration rate of 1230 L / m2» min. with a bed compression of 15%.

The ability to compress the filter media is a significant factor in the operation of the filter of the invention as described. The porosity of the bed can be modified to meet the characteristics of the affluent liquid. The porosity of the bed can be altered without significantly affecting the filtration efficiency to delay the onset of an unacceptable load loss through the filtration medium, thus additionally extending the filter life between the countercurrent wash cycles. Because the bed is highly porous, significantly higher filtration rates can be used compared to conventional granulated filtration media which filter from 80 to 410 L / m2 »min. In contrast, in the practice of the invention, filtration rates can be achieved from 820 to 1230 L / m2 • min. The optimum filtration rate seems to be in the range of 820 to 1230 L / m2 »min. with a bed compression of approximately 15 to 30 percent. Effluent turbidity values of 2 NTU or less can be achieved without the addition of chemicals for affluent turbidity values of up to about 8 NTU when the flow is between 820 and 1230 L / m2 »min. with a bed compression ratio between 15 and 40 percent. The secondary effluent can be used as the backwash water. It was observed that a flow rate of 410 L / m2 »min. It is enough to clean the filtration medium. The percentage of backwash water required at the filtration rates of 820 and 1230 L / m2 »min. and with bed compression values between 20 and 30 percent varied from 1.1 to 3.1 percent, which is extremely efficient compared to conventional technologies.

Claims (32)

NOVELTY OF THE INVENTION CLAIMS

1. - A filtration apparatus composed of: a filter housing having a fluid inlet and a fluid outlet; a filtration medium with porosity and adjustable manifold size disposed in a filtration bed within said filter housing between said fluid inlet and said fluid outlet; means for adjusting the porosity and the size of the collector of the filtration medium, said means including means for compressing the filtration medium in a compression gradient proceeding from the most compressed to the least compressed in a direction opposite to the fluid flow of so that the filtration proceeds in one direction from the more porous filter to the less porous filter.

2. An apparatus according to claim 1, further characterized in that the means for compressing said filtration means comprise: a first fixed perforated panel mounted inside said apparatus; a second movable perforated panel mounted within said apparatus and separated above said first perforated panel; and means for selectively moving said second perforated panel movably mounted toward and away from said first perforated panel, said means being located above said second perforated panel.

3. - An apparatus according to claim 2, further characterized in that it comprises means for agitating said filtration means in an uncompressed condition to clean said filtering means.

4. An apparatus according to claim 1, further characterized in that said fluid inlet is disposed below said fluid outlet and said filter is operated in an ascending mode.

5. The apparatus according to claim 1, further characterized in that said means for adjusting the porosity and size of the collector of the filtration medium can be adjusted during filtration.

6. The apparatus according to claim 1, further characterized in that said filtration means is a means of filtering compressible fibrous lumps.

7. The apparatus according to claim 1, further characterized in that said filter bed has a porosity of approximately 92 to 94 percent prior to compression and a porosity from 87 to 90 percent when compressed.

8. The apparatus according to claim 1, further characterized in that said filter bed, prior to compression, has a depth of at least about 760 mm.

9. - The apparatus according to claim 1, further characterized in that said apparatus is operable for filtration at a fluid flow rate of 205 to 1230 L / m2 »min. with a bed compression ratio from 0 to 40 percent, and a countercurrent wash rate from 1 to 6 percent based on the total fluid passing through the filter.

10. The apparatus according to claim 9, further characterized in that said fluid flow rate ranges from 410 to 1230 L / m2 »min.

11. The apparatus according to claim 9, further characterized in that said fluid flow rate ranges from 820 to 1230 L / m2 »min.

12. The filtering apparatus comprising: a filter housing having a fluid inlet and a fluid outlet, further characterized in that said fluid inlet is disposed below said fluid outlet and said fluid is operated in a manner upflow; the porosity filtration medium and adjustable manifold size disposed in a filtration bed within said filter housing between said fluid inlet and said fluid outlet; a first fixed perforated panel mounted within said apparatus; a second movable perforated panel mounted within said apparatus and separated above said first perforated panel; and means for selectively moving said second movable perforated panel towards and away from said first perforated panel, said means being located above said second perforated panel, whereby the porosity of said filtration bed can be adjusted by means of compression of the medium.

13. The apparatus according to claim 12, further characterized in that the porosity of said filter bed can be adjusted from a porosity of approximately 92 to 94 percent prior to compression to a porosity of 87 to 90 percent when compressed .

14. The apparatus according to claim 1, further characterized in that said apparatus is operable for filtration at a fluid flow rate of between 820 and 1230 L / m2 »min., With a bed compression ratio of approximately 15. at 40 percent and a countercurrent wash rate from 1 to 6 percent based on the total fluid that passes through the filter.

15. The filtering apparatus for wastewater treatment comprising: an inlet for introducing wastewater into said apparatus so that it flows upwards through said apparatus; an outlet to discharge the filtered waste water from said apparatus; a first perforated panel mounted non-movably within said apparatus; a second perforated panel mounted movably within said apparatus and separated above said first perforated panel; means for selectively moving said second perforated panel movably mounted towards and away from said first perforated panel, said means being located above said second perforated panel; a filtering medium of compressible fibrous lumps disposed between said first and second perforated panels and defining a filtration bed, further characterized in that said compressible medium is compressed for filtration in a gradient that proceeds from the most compressed to the least compressed in one opposite direction to the flow of fluid so that the filtration proceeds in a direction from a more porous filtration bed towards a less porous filtration bed, and characterized in that said filtration bed is expanded for cleaning; and means for introducing a gas into said waste water when said filter bed is expanded for cleaning.

16. The apparatus in accordance with the claim 15, further characterized in that said inlet further comprises a plenum for uniformly distributing the waste water through said first perforated panel.

17. The apparatus according to claim 16, further characterized in that said apparatus is operable for filtering to reduce the turbidity of effluent wastewater from 8 NTU to about 2 NTU at a residual water flow rate from 820 to 1230 L / m2 * min with a bed compression ratio from 15 to 40%, and a countercurrent wash rate from 1 to 6% based on the total wastewater that passes through the filter.

18. The apparatus according to claim 17, further characterized in that the countercurrent wash flow rate ranges from 1 to 3% based on the total residual water passing through the filter.

19. A process for filtering a fluid comprising the steps of: a) passing fluid through a filtration bed composed of a compressible filtration medium; b) compressing the filtration medium to define a porosity gradient in the filtration bed that proceeds from the most porous to the least porous in a direction opposite to the flow of the fluid so that the filtration proceeds in one direction from the filtration bed further porous towards the less porous filtration bed; and c) periodically expanding the filtration bed while continuously passing fluid through the filtration bed to clean the filtration medium.

20. The method according to claim 19, further characterized in that the fluid is a liquid and gas is injected into the liquid prior to entering the filtration bed for further cleaning of the medium.

21. The process according to claim 19, further characterized in that it comprises the step of progressively removing smaller particles from the fluid as the filtration proceeds from a more porous medium to a less porous medium.

22. The method according to claim 19, further characterized in that it comprises the step of altering the compression of the medium during filtration in response to the conditions of the incoming fluid.

23. The method according to claim 19, further characterized in that it comprises the steps of: monitoring the pressure loss across the filtration bed and altering the compression of the medium during filtration to reduce the pressure loss and to increase the time between periodic cleaning operations.

24. A method for filtering a liquid to remove particles thereof comprising the steps of: a) passing the liquid through a filtration bed composed of a filter medium of compressible fibrous lumps; b) compressing the filtration medium to define a porosity gradient in the filtration bed that proceeds from the most porous to the least porous in a direction opposite to the flow of the liquid so that the filtration proceeds in one direction from a filtration bed more porous towards a less porous filtration bed; c) progressively removing the smaller particles from the fluid as the filtration proceeds from a more porous filtration medium to a less porous filtration medium; d) monitor the loss of charge through the filtration bed; e) Periodically expanding the filtration bed when a maximum head loss has been reached while continuously passing the liquid through the filtration bed to clean the filtration medium.

25. The process according to claim 24, further characterized in that the liquid is passed through the expanded filtration bed at a rate that is between 1 to 6% of the total flow of the liquid through the filtration bed.

26. The method according to claim 1, further characterized in that the filtration bed is compressed at a maximum compression ratio from 0 to 40%, the liquid is passed through the compressed filtration bed at a flow rate from 205 to 1230 L / m2. min, and the countercurrent wash liquid is passed through the filter at a countercurrent wash rate from 1 to 6% based on the total fluid passing through the filter.

27. The process according to claim 24, further characterized in that the filtration bed is compressed from a porosity of about 92 to 94% at a minimum porosity of 87 to 90%. 28.- The method according to claim 24, further characterized in that the maximum removal efficiency is achieved at a bed compression of 40% with a liquid flow rate of 820 L / m2 • min and with a bed compression 30% at a flow rate of 1230. L / m2 »min 29.- A process for the tertiary treatment of wastewater that includes the steps of: a) treating the wastewater in an activated sludge reactor to provide an effluent primary; b) treating the primary effluent in a clarifier to provide a secondary effluent, c) supplying the secondary effluent to the filtration apparatus according to claim 15 and filtering the secondary effluent to provide a tertiary effluent, 30.- The procedure in accordance with claim 29, further characterized in that the filtration apparatus is operable for filtration to reduce the turbidity of effluent wastewater from 8 NTU to about 2 NTU with a residual water flow rate from 820 to 1230 L / m2 »min, with a compression ratio of the bed, from 15 to 40%, and a backwashing rate from 1 to 6% based on the total residual water that passes through the filter. 31.- The method according to claim 30 further characterized in that the countercurrent wash flow rate ranges from 1 to 3% based on the total waste water passing through the filter. 32. The method according to claim 30, further characterized in that the speed of water production of the filter is at least 760 mm. of uncompressed depth and with an effluent quality of 2 NTU or less based on the quality of a tributary of up to 8 NTU is around 1, 000,000 L / m2"day.